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DRBD.CONF(5)		      Configuration Files		  DRBD.CONF(5)

NAME
       drbd.conf - Configuration file for DRBD's devices .

INTRODUCTION
       The file /etc/drbd.conf is read by drbdadm.

       The file format was designed as to allow to have a verbatim copy of the
       file on both nodes of the cluster. It is highly recommended to do so in
       order to keep your configuration manageable. The file /etc/drbd.conf
       should be the same on both nodes of the cluster. Changes to
       /etc/drbd.conf do not apply immediately.

       By convention the main config contains two include statements. The
       first one includes the file /etc/drbd.d/global_common.conf, the second
       one all file with a .res suffix.

       alice uses /dev/drbd1 as devices for its application, and /dev/sda7 as
       low-level storage for the data. The IP addresses are used to specify
       the networking interfaces to be used. An eventually running resync
       process should use about 10MByte/second of IO bandwidth. This sync-rate
       statement is valid for volume 0, but would also be valid for further
       volumes. In this example it assigns full 10MByte/second to each volume.

       There may be multiple resource sections in a single drbd.conf file. For
       more examples, please have a look at the DRBD User's Guide[1].

FILE FORMAT
       The file consists of sections and parameters. A section begins with a
       keyword, sometimes an additional name, and an opening brace (“{”). A
       section ends with a closing brace (“}”. The braces enclose the
       parameters.

       section [name] { parameter value; [...] }

       A parameter starts with the identifier of the parameter followed by
       whitespace. Every subsequent character is considered as part of the
       parameter's value. A special case are Boolean parameters which consist
       only of the identifier. Parameters are terminated by a semicolon (“;”).

       Some parameter values have default units which might be overruled by K,
       M or G. These units are defined in the usual way (K = 2^10 = 1024, M =
       1024 K, G = 1024 M).

       Comments may be placed into the configuration file and must begin with
       a hash sign (“#”). Subsequent characters are ignored until the end of
       the line.

   Sections
       skip
	   Comments out chunks of text, even spanning more than one line.
	   Characters between the keyword skip and the opening brace (“{”) are
	   ignored. Everything enclosed by the braces is skipped. This comes
	   in handy, if you just want to comment out some 'resource [name]
	   {...}' section: just precede it with 'skip'.

       global
	   Configures some global parameters. Currently only minor-count,
	   dialog-refresh, disable-ip-verification and usage-count are allowed
	   here. You may only have one global section, preferably as the first
	   section.

       common
	   All resources inherit the options set in this section. The common
	   section might have a startup, a options, a handlers, a net and a
	   disk section.

       resource name
	   Configures a DRBD resource. Each resource section needs to have two
	   (or more) on host sections and may have a startup, a options, a
	   handlers, a net and a disk section. It might contain volumes
	   sections.

       on host-name
	   Carries the necessary configuration parameters for a DRBD device of
	   the enclosing resource.  host-name is mandatory and must match the
	   Linux host name (uname -n) of one of the nodes. You may list more
	   than one host name here, in case you want to use the same
	   parameters on several hosts (you'd have to move the IP around
	   usually). Or you may list more than two such sections.

		    resource r1 {
			 protocol C;
			 device minor 1;
			 meta-disk internal;

			 on alice bob {
			      address 10.2.2.100:7801;
			      disk /dev/mapper/some-san;
			 }
			 on charlie {
			      address 10.2.2.101:7801;
			      disk /dev/mapper/other-san;
			 }
			 on daisy {
			      address 10.2.2.103:7801;
			      disk /dev/mapper/other-san-as-seen-from-daisy;
			 }
		    }

	   See also the floating section keyword. Required statements in this
	   section: address and volume. Note for backward compatibility and
	   convenience it is valid to embed the statements of a single volume
	   directly into the host section.

       volume vnr
	   Defines a volume within a connection. The minor numbers of a
	   replicated volume might be different on different hosts, the volume
	   number (vnr) is what groups them together. Required parameters in
	   this section: device, disk, meta-disk.

       stacked-on-top-of resource
	   For a stacked DRBD setup (3 or 4 nodes), a stacked-on-top-of is
	   used instead of an on section. Required parameters in this section:
	   device and address.

       floating AF addr:port
	   Carries the necessary configuration parameters for a DRBD device of
	   the enclosing resource. This section is very similar to the on
	   section. The difference to the on section is that the matching of
	   the host sections to machines is done by the IP-address instead of
	   the node name. Required parameters in this section: device, disk,
	   meta-disk, all of which may be inherited from the resource section,
	   in which case you may shorten this section down to just the address
	   identifier.

		    resource r2 {
			 protocol C;
			 device minor 2;
			 disk	   /dev/sda7;
			 meta-disk internal;

			 # short form, device, disk and meta-disk inherited
			 floating 10.1.1.31:7802;

			 # longer form, only device inherited
			 floating 10.1.1.32:7802 {
			      disk /dev/sdb;
			      meta-disk /dev/sdc8;
			 }
		    }

       disk
	   This section is used to fine tune DRBD's properties in respect to
	   the low level storage. Please refer to drbdsetup(8) for detailed
	   description of the parameters. Optional parameters: on-io-error,
	   size, fencing, disk-barrier, disk-flushes, disk-drain, md-flushes,
	   max-bio-bvecs, resync-rate, resync-after, al-extents, al-updates,
	   c-plan-ahead, c-fill-target, c-delay-target, c-max-rate,
	   c-min-rate, disk-timeout, read-balancing.

       net
	   This section is used to fine tune DRBD's properties. Please refer
	   to drbdsetup(8) for a detailed description of this section's
	   parameters. Optional parameters: protocol, sndbuf-size,
	   rcvbuf-size, timeout, connect-int, ping-int, ping-timeout,
	   max-buffers, max-epoch-size, ko-count, allow-two-primaries,
	   cram-hmac-alg, shared-secret, after-sb-0pri, after-sb-1pri,
	   after-sb-2pri, data-integrity-alg, no-tcp-cork, on-congestion,
	   congestion-fill, congestion-extents, verify-alg, use-rle,
	   csums-alg.

       startup
	   This section is used to fine tune DRBD's properties. Please refer
	   to drbdsetup(8) for a detailed description of this section's
	   parameters. Optional parameters: wfc-timeout, degr-wfc-timeout,
	   outdated-wfc-timeout, wait-after-sb, stacked-timeouts and
	   become-primary-on.

       options
	   This section is used to fine tune the behaviour of the resource
	   object. Please refer to drbdsetup(8) for a detailed description of
	   this section's parameters. Optional parameters: cpu-mask, and
	   on-no-data-accessible.

       handlers
	   In this section you can define handlers (executables) that are
	   started by the DRBD system in response to certain events. Optional
	   parameters: pri-on-incon-degr, pri-lost-after-sb, pri-lost,
	   fence-peer (formerly oudate-peer), local-io-error,
	   initial-split-brain, split-brain, before-resync-target,
	   after-resync-target.

	   The interface is done via environment variables:

	   ·   DRBD_RESOURCE is the name of the resource

	   ·   DRBD_MINOR is the minor number of the DRBD device, in decimal.

	   ·   DRBD_CONF is the path to the primary configuration file; if you
	       split your configuration into multiple files (e.g. in
	       /etc/drbd.conf.d/), this will not be helpful.

	   ·   DRBD_PEER_AF , DRBD_PEER_ADDRESS , DRBD_PEERS are the address
	       family (e.g.  ipv6), the peer's address and hostnames.

	   DRBD_PEER is deprecated.

	   Please note that not all of these might be set for all handlers,
	   and that some values might not be useable for a floating
	   definition.

   Parameters
       minor-count count
	   may be a number from 1 to 1048575.

	   Minor-count is a sizing hint for DRBD. It helps to right-size
	   various memory pools. It should be set in the in the same order of
	   magnitude than the actual number of minors you use. Per default the
	   module loads with 11 more resources than you have currently in your
	   config but at least 32.

       dialog-refresh time
	   may be 0 or a positive number.

	   The user dialog redraws the second count every time seconds (or
	   does no redraws if time is 0). The default value is 1.

       disable-ip-verification
	   Use disable-ip-verification if, for some obscure reasons, drbdadm
	   can/might not use ip or ifconfig to do a sanity check for the IP
	   address. You can disable the IP verification with this option.

       usage-count val
	   Please participate in DRBD's online usage counter[2]. The most
	   convenient way to do so is to set this option to yes. Valid options
	   are: yes, no and ask.

       protocol prot-id
	   On the TCP/IP link the specified protocol is used. Valid protocol
	   specifiers are A, B, and C.

	   Protocol A: write IO is reported as completed, if it has reached
	   local disk and local TCP send buffer.

	   Protocol B: write IO is reported as completed, if it has reached
	   local disk and remote buffer cache.

	   Protocol C: write IO is reported as completed, if it has reached
	   both local and remote disk.

       device name minor nr
	   The name of the block device node of the resource being described.
	   You must use this device with your application (file system) and
	   you must not use the low level block device which is specified with
	   the disk parameter.

	   One can ether omit the name or minor and the minor number. If you
	   omit the name a default of /dev/drbdminor will be used.

	   Udev will create additional symlinks in /dev/drbd/by-res and
	   /dev/drbd/by-disk.

       disk name
	   DRBD uses this block device to actually store and retrieve the
	   data. Never access such a device while DRBD is running on top of
	   it. This also holds true for dumpe2fs(8) and similar commands.

       address AF addr:port
	   A resource needs one IP address per device, which is used to wait
	   for incoming connections from the partner device respectively to
	   reach the partner device.  AF must be one of ipv4, ipv6, ssocks or
	   sdp (for compatibility reasons sci is an alias for ssocks). It may
	   be omited for IPv4 addresses. The actual IPv6 address that follows
	   the ipv6 keyword must be placed inside brackets: ipv6
	   [fd01:2345:6789:abcd::1]:7800.

	   Each DRBD resource needs a TCP port which is used to connect to the
	   node's partner device. Two different DRBD resources may not use the
	   same addr:port combination on the same node.

       meta-disk internal, meta-disk device, meta-disk device [index]
	   Internal means that the last part of the backing device is used to
	   store the meta-data. The size of the meta-data is computed based on
	   the size of the device.

	   When a device is specified, either with or without an index, DRBD
	   stores the meta-data on this device. Without index, the size of the
	   meta-data is determined by the size of the data device. This is
	   usually used with LVM, which allows to have many variable sized
	   block devices. The meta-data size is 36kB + Backing-Storage-size /
	   32k, rounded up to the next 4kb boundary. (Rule of the thumb:
	   32kByte per 1GByte of storage, rounded up to the next MB.)

	   When an index is specified, each index number refers to a fixed
	   slot of meta-data of 128 MB, which allows a maximum data size of 4
	   GB. This way, multiple DBRD devices can share the same meta-data
	   device. For example, if /dev/sde6[0] and /dev/sde6[1] are used,
	   /dev/sde6 must be at least 256 MB big. Because of the hard size
	   limit, use of meta-disk indexes is discouraged.

       on-io-error handler
	   is taken, if the lower level device reports io-errors to the upper
	   layers.

	   handler may be pass_on, call-local-io-error or detach.

	   pass_on: The node downgrades the disk status to inconsistent, marks
	   the erroneous block as inconsistent in the bitmap and retries the
	   IO on the remote node.

	   call-local-io-error: Call the handler script local-io-error.

	   detach: The node drops its low level device, and continues in
	   diskless mode.

       fencing fencing_policy
	   By fencing we understand preventive measures to avoid situations
	   where both nodes are primary and disconnected (AKA split brain).

	   Valid fencing policies are:

	   dont-care
	       This is the default policy. No fencing actions are taken.

	   resource-only
	       If a node becomes a disconnected primary, it tries to fence the
	       peer's disk. This is done by calling the fence-peer handler.
	       The handler is supposed to reach the other node over
	       alternative communication paths and call 'drbdadm outdate res'
	       there.

	   resource-and-stonith
	       If a node becomes a disconnected primary, it freezes all its IO
	       operations and calls its fence-peer handler. The fence-peer
	       handler is supposed to reach the peer over alternative
	       communication paths and call 'drbdadm outdate res' there. In
	       case it cannot reach the peer it should stonith the peer. IO is
	       resumed as soon as the situation is resolved. In case your
	       handler fails, you can resume IO with the resume-io command.

       disk-barrier, disk-flushes, disk-drain
	   DRBD has four implementations to express write-after-write
	   dependencies to its backing storage device. DRBD will use the first
	   method that is supported by the backing storage device and that is
	   not disabled. By default the flush method is used.

	   Since drbd-8.4.2 disk-barrier is disabled by default because since
	   linux-2.6.36 (or 2.6.32 RHEL6) there is no reliable way to
	   determine if queuing of IO-barriers works.  Dangerous only enable
	   if you are told so by one that knows for sure.

	   When selecting the method you should not only base your decision on
	   the measurable performance. In case your backing storage device has
	   a volatile write cache (plain disks, RAID of plain disks) you
	   should use one of the first two. In case your backing storage
	   device has battery-backed write cache you may go with option 3.
	   Option 4 (disable everything, use "none") is dangerous on most IO
	   stacks, may result in write-reordering, and if so, can
	   theoretically be the reason for data corruption, or disturb the
	   DRBD protocol, causing spurious disconnect/reconnect cycles.	 Do
	   not use no-disk-drain.

	   Unfortunately device mapper (LVM) might not support barriers.

	   The letter after "wo:" in /proc/drbd indicates with method is
	   currently in use for a device: b, f, d, n. The implementations are:

	   barrier
	       The first requires that the driver of the backing storage
	       device support barriers (called 'tagged command queuing' in
	       SCSI and 'native command queuing' in SATA speak). The use of
	       this method can be enabled by setting the disk-barrier options
	       to yes.

	   flush
	       The second requires that the backing device support disk
	       flushes (called 'force unit access' in the drive vendors
	       speak). The use of this method can be disabled setting
	       disk-flushes to no.

	   drain
	       The third method is simply to let write requests drain before
	       write requests of a new reordering domain are issued. This was
	       the only implementation before 8.0.9.

	   none
	       The fourth method is to not express write-after-write
	       dependencies to the backing store at all, by also specifying
	       no-disk-drain. This is dangerous on most IO stacks, may result
	       in write-reordering, and if so, can theoretically be the reason
	       for data corruption, or disturb the DRBD protocol, causing
	       spurious disconnect/reconnect cycles.  Do not use
	       no-disk-drain.

       md-flushes
	   Disables the use of disk flushes and barrier BIOs when accessing
	   the meta data device. See the notes on disk-flushes.

       max-bio-bvecs
	   In some special circumstances the device mapper stack manages to
	   pass BIOs to DRBD that violate the constraints that are set forth
	   by DRBD's merge_bvec() function and which have more than one bvec.
	   A known example is: phys-disk -> DRBD -> LVM -> Xen -> misaligned
	   partition (63) -> DomU FS. Then you might see "bio would need to,
	   but cannot, be split:" in the Dom0's kernel log.

	   The best workaround is to proper align the partition within the VM
	   (E.g. start it at sector 1024). This costs 480 KiB of storage.
	   Unfortunately the default of most Linux partitioning tools is to
	   start the first partition at an odd number (63). Therefore most
	   distribution's install helpers for virtual linux machines will end
	   up with misaligned partitions. The second best workaround is to
	   limit DRBD's max bvecs per BIO (= max-bio-bvecs) to 1, but that
	   might cost performance.

	   The default value of max-bio-bvecs is 0, which means that there is
	   no user imposed limitation.

       disk-timeout
	   If the driver of the lower_device does not finish an IO request
	   within disk_timeout, DRBD considers the disk as failed. If DRBD is
	   connected to a remote host, it will reissue local pending IO
	   requests to the peer, and ship all new IO requests to the peer
	   only. The disk state advances to diskless, as soon as the backing
	   block device has finished all IO requests.

	   The default value of is 0, which means that no timeout is enforced.
	   The default unit is 100ms. This option is available since 8.3.12.

       read-balancing method
	   The supported methods for load balancing of read requests are
	   prefer-local, prefer-remote, round-robin, least-pending,
	   when-congested-remote, 32K-striping, 64K-striping, 128K-striping,
	   256K-striping, 512K-striping and 1M-striping.

	   The default value of is prefer-local. This option is available
	   since 8.4.1.

       sndbuf-size size
	   is the size of the TCP socket send buffer. The default value is 0,
	   i.e. autotune. You can specify smaller or larger values. Larger
	   values are appropriate for reasonable write throughput with
	   protocol A over high latency networks. Values below 32K do not make
	   sense. Since 8.0.13 resp. 8.2.7, setting the size value to 0 means
	   that the kernel should autotune this.

       rcvbuf-size size
	   is the size of the TCP socket receive buffer. The default value is
	   0, i.e. autotune. You can specify smaller or larger values. Usually
	   this should be left at its default. Setting the size value to 0
	   means that the kernel should autotune this.

       timeout time
	   If the partner node fails to send an expected response packet
	   within time tenths of a second, the partner node is considered dead
	   and therefore the TCP/IP connection is abandoned. This must be
	   lower than connect-int and ping-int. The default value is 60 = 6
	   seconds, the unit 0.1 seconds.

       connect-int time
	   In case it is not possible to connect to the remote DRBD device
	   immediately, DRBD keeps on trying to connect. With this option you
	   can set the time between two retries. The default value is 10
	   seconds, the unit is 1 second.

       ping-int time
	   If the TCP/IP connection linking a DRBD device pair is idle for
	   more than time seconds, DRBD will generate a keep-alive packet to
	   check if its partner is still alive. The default is 10 seconds, the
	   unit is 1 second.

       ping-timeout time
	   The time the peer has time to answer to a keep-alive packet. In
	   case the peer's reply is not received within this time period, it
	   is considered as dead. The default value is 500ms, the default unit
	   are tenths of a second.

       max-buffers number
	   Maximum number of requests to be allocated by DRBD. Unit is
	   PAGE_SIZE, which is 4 KiB on most systems. The minimum is hard
	   coded to 32 (=128 KiB). For high-performance installations it might
	   help if you increase that number. These buffers are used to hold
	   data blocks while they are written to disk.

       ko-count number
	   In case the secondary node fails to complete a single write request
	   for count times the timeout, it is expelled from the cluster. (I.e.
	   the primary node goes into StandAlone mode.) The default value is
	   0, which disables this feature.

       max-epoch-size number
	   The highest number of data blocks between two write barriers. If
	   you set this smaller than 10, you might decrease your performance.

       allow-two-primaries
	   With this option set you may assign the primary role to both nodes.
	   You only should use this option if you use a shared storage file
	   system on top of DRBD. At the time of writing the only ones are:
	   OCFS2 and GFS. If you use this option with any other file system,
	   you are going to crash your nodes and to corrupt your data!

       unplug-watermark number
	   When the number of pending write requests on the standby
	   (secondary) node exceeds the unplug-watermark, we trigger the
	   request processing of our backing storage device. Some storage
	   controllers deliver better performance with small values, others
	   deliver best performance when the value is set to the same value as
	   max-buffers. Minimum 16, default 128, maximum 131072.

       cram-hmac-alg
	   You need to specify the HMAC algorithm to enable peer
	   authentication at all. You are strongly encouraged to use peer
	   authentication. The HMAC algorithm will be used for the challenge
	   response authentication of the peer. You may specify any digest
	   algorithm that is named in /proc/crypto.

       shared-secret
	   The shared secret used in peer authentication. May be up to 64
	   characters. Note that peer authentication is disabled as long as no
	   cram-hmac-alg (see above) is specified.

       after-sb-0pri  policy
	   possible policies are:

	   disconnect
	       No automatic resynchronization, simply disconnect.

	   discard-younger-primary
	       Auto sync from the node that was primary before the split-brain
	       situation happened.

	   discard-older-primary
	       Auto sync from the node that became primary as second during
	       the split-brain situation.

	   discard-zero-changes
	       In case one node did not write anything since the split brain
	       became evident, sync from the node that wrote something to the
	       node that did not write anything. In case none wrote anything
	       this policy uses a random decision to perform a "resync" of 0
	       blocks. In case both have written something this policy
	       disconnects the nodes.

	   discard-least-changes
	       Auto sync from the node that touched more blocks during the
	       split brain situation.

	   discard-node-NODENAME
	       Auto sync to the named node.

       after-sb-1pri  policy
	   possible policies are:

	   disconnect
	       No automatic resynchronization, simply disconnect.

	   consensus
	       Discard the version of the secondary if the outcome of the
	       after-sb-0pri algorithm would also destroy the current
	       secondary's data. Otherwise disconnect.

	   violently-as0p
	       Always take the decision of the after-sb-0pri algorithm, even
	       if that causes an erratic change of the primary's view of the
	       data. This is only useful if you use a one-node FS (i.e. not
	       OCFS2 or GFS) with the allow-two-primaries flag, AND if you
	       really know what you are doing. This is DANGEROUS and MAY CRASH
	       YOUR MACHINE if you have an FS mounted on the primary node.

	   discard-secondary
	       Discard the secondary's version.

	   call-pri-lost-after-sb
	       Always honor the outcome of the after-sb-0pri algorithm. In
	       case it decides the current secondary has the right data, it
	       calls the "pri-lost-after-sb" handler on the current primary.

       after-sb-2pri  policy
	   possible policies are:

	   disconnect
	       No automatic resynchronization, simply disconnect.

	   violently-as0p
	       Always take the decision of the after-sb-0pri algorithm, even
	       if that causes an erratic change of the primary's view of the
	       data. This is only useful if you use a one-node FS (i.e. not
	       OCFS2 or GFS) with the allow-two-primaries flag, AND if you
	       really know what you are doing. This is DANGEROUS and MAY CRASH
	       YOUR MACHINE if you have an FS mounted on the primary node.

	   call-pri-lost-after-sb
	       Call the "pri-lost-after-sb" helper program on one of the
	       machines. This program is expected to reboot the machine, i.e.
	       make it secondary.

       always-asbp
	   Normally the automatic after-split-brain policies are only used if
	   current states of the UUIDs do not indicate the presence of a third
	   node.

	   With this option you request that the automatic after-split-brain
	   policies are used as long as the data sets of the nodes are somehow
	   related. This might cause a full sync, if the UUIDs indicate the
	   presence of a third node. (Or double faults led to strange UUID
	   sets.)

       rr-conflict  policy
	   This option helps to solve the cases when the outcome of the resync
	   decision is incompatible with the current role assignment in the
	   cluster.

	   disconnect
	       No automatic resynchronization, simply disconnect.

	   violently
	       Sync to the primary node is allowed, violating the assumption
	       that data on a block device are stable for one of the nodes.
	       Dangerous, do not use.

	   call-pri-lost
	       Call the "pri-lost" helper program on one of the machines. This
	       program is expected to reboot the machine, i.e. make it
	       secondary.

       data-integrity-alg  alg
	   DRBD can ensure the data integrity of the user's data on the
	   network by comparing hash values. Normally this is ensured by the
	   16 bit checksums in the headers of TCP/IP packets.

	   This option can be set to any of the kernel's data digest
	   algorithms. In a typical kernel configuration you should have at
	   least one of md5, sha1, and crc32c available. By default this is
	   not enabled.

	   See also the notes on data integrity.

       tcp-cork
	   DRBD usually uses the TCP socket option TCP_CORK to hint to the
	   network stack when it can expect more data, and when it should
	   flush out what it has in its send queue. It turned out that there
	   is at least one network stack that performs worse when one uses
	   this hinting method. Therefore we introducted this option. By
	   setting tcp-cork to no you can disable the setting and clearing of
	   the TCP_CORK socket option by DRBD.

       on-congestion congestion_policy, congestion-fill fill_threshold,
       congestion-extents active_extents_threshold
	   By default DRBD blocks when the available TCP send queue becomes
	   full. That means it will slow down the application that generates
	   the write requests that cause DRBD to send more data down that TCP
	   connection.

	   When DRBD is deployed with DRBD-proxy it might be more desirable
	   that DRBD goes into AHEAD/BEHIND mode shortly before the send queue
	   becomes full. In AHEAD/BEHIND mode DRBD does no longer replicate
	   data, but still keeps the connection open.

	   The advantage of the AHEAD/BEHIND mode is that the application is
	   not slowed down, even if DRBD-proxy's buffer is not sufficient to
	   buffer all write requests. The downside is that the peer node falls
	   behind, and that a resync will be necessary to bring it back into
	   sync. During that resync the peer node will have an inconsistent
	   disk.

	   Available congestion_policys are block and pull-ahead. The default
	   is block.  Fill_threshold might be in the range of 0 to 10GiBytes.
	   The default is 0 which disables the check.
	   Active_extents_threshold has the same limits as al-extents.

	   The AHEAD/BEHIND mode and its settings are available since DRBD
	   8.3.10.

       wfc-timeout time
	   Wait for connection timeout.	 The init script drbd(8) blocks the
	   boot process until the DRBD resources are connected. When the
	   cluster manager starts later, it does not see a resource with
	   internal split-brain. In case you want to limit the wait time, do
	   it here. Default is 0, which means unlimited. The unit is seconds.

       degr-wfc-timeout time
	   Wait for connection timeout, if this node was a degraded cluster.
	   In case a degraded cluster (= cluster with only one node left) is
	   rebooted, this timeout value is used instead of wfc-timeout,
	   because the peer is less likely to show up in time, if it had been
	   dead before. Value 0 means unlimited.

       outdated-wfc-timeout time
	   Wait for connection timeout, if the peer was outdated. In case a
	   degraded cluster (= cluster with only one node left) with an
	   outdated peer disk is rebooted, this timeout value is used instead
	   of wfc-timeout, because the peer is not allowed to become primary
	   in the meantime. Value 0 means unlimited.

       wait-after-sb
	   By setting this option you can make the init script to continue to
	   wait even if the device pair had a split brain situation and
	   therefore refuses to connect.

       become-primary-on node-name
	   Sets on which node the device should be promoted to primary role by
	   the init script. The node-name might either be a host name or the
	   keyword both. When this option is not set the devices stay in
	   secondary role on both nodes. Usually one delegates the role
	   assignment to a cluster manager (e.g. heartbeat).

       stacked-timeouts
	   Usually wfc-timeout and degr-wfc-timeout are ignored for stacked
	   devices, instead twice the amount of connect-int is used for the
	   connection timeouts. With the stacked-timeouts keyword you disable
	   this, and force DRBD to mind the wfc-timeout and degr-wfc-timeout
	   statements. Only do that if the peer of the stacked resource is
	   usually not available or will usually not become primary. By using
	   this option incorrectly, you run the risk of causing unexpected
	   split brain.

       resync-rate rate
	   To ensure a smooth operation of the application on top of DRBD, it
	   is possible to limit the bandwidth which may be used by background
	   synchronizations. The default is 250 KB/sec, the default unit is
	   KB/sec. Optional suffixes K, M, G are allowed.

       use-rle
	   During resync-handshake, the dirty-bitmaps of the nodes are
	   exchanged and merged (using bit-or), so the nodes will have the
	   same understanding of which blocks are dirty. On large devices, the
	   fine grained dirty-bitmap can become large as well, and the bitmap
	   exchange can take quite some time on low-bandwidth links.

	   Because the bitmap typically contains compact areas where all bits
	   are unset (clean) or set (dirty), a simple run-length encoding
	   scheme can considerably reduce the network traffic necessary for
	   the bitmap exchange.

	   For backward compatibilty reasons, and because on fast links this
	   possibly does not improve transfer time but consumes cpu cycles,
	   this defaults to off.

       resync-after res-name
	   By default, resynchronization of all devices would run in parallel.
	   By defining a resync-after dependency, the resynchronization of
	   this resource will start only if the resource res-name is already
	   in connected state (i.e., has finished its resynchronization).

       al-extents extents
	   DRBD automatically performs hot area detection. With this parameter
	   you control how big the hot area (= active set) can get. Each
	   extent marks 4M of the backing storage (= low-level device). In
	   case a primary node leaves the cluster unexpectedly, the areas
	   covered by the active set must be resynced upon rejoining of the
	   failed node. The data structure is stored in the meta-data area,
	   therefore each change of the active set is a write operation to the
	   meta-data device. A higher number of extents gives longer resync
	   times but less updates to the meta-data. The default number of
	   extents is 1237. (Minimum: 7, Maximum: 65534)

	   Note that the effective maximum may be smaller, depending on how
	   you created the device meta data, see also drbdmeta(8). The
	   effective maximum is 919 * (available on-disk activity-log
	   ring-buffer area/4kB -1), the default 32kB ring-buffer effects a
	   maximum of 6433 (covers more than 25 GiB of data). We recommend to
	   keep this well within the amount your backend storage and
	   replication link are able to resync inside of about 5 minutes.

       al-updates {yes | no}
	   DRBD's activity log transaction writing makes it possible, that
	   after the crash of a primary node a partial (bit-map based) resync
	   is sufficient to bring the node back to up-to-date. Setting
	   al-updates to no might increase normal operation performance but
	   causes DRBD to do a full resync when a crashed primary gets
	   reconnected. The default value is yes.

       verify-alg hash-alg
	   During online verification (as initiated by the verify
	   sub-command), rather than doing a bit-wise comparison, DRBD applies
	   a hash function to the contents of every block being verified, and
	   compares that hash with the peer. This option defines the hash
	   algorithm being used for that purpose. It can be set to any of the
	   kernel's data digest algorithms. In a typical kernel configuration
	   you should have at least one of md5, sha1, and crc32c available. By
	   default this is not enabled; you must set this option explicitly in
	   order to be able to use on-line device verification.

	   See also the notes on data integrity.

       csums-alg hash-alg
	   A resync process sends all marked data blocks from the source to
	   the destination node, as long as no csums-alg is given. When one is
	   specified the resync process exchanges hash values of all marked
	   blocks first, and sends only those data blocks that have different
	   hash values.

	   This setting is useful for DRBD setups with low bandwidth links.
	   During the restart of a crashed primary node, all blocks covered by
	   the activity log are marked for resync. But a large part of those
	   will actually be still in sync, therefore using csums-alg will
	   lower the required bandwidth in exchange for CPU cycles.

       c-plan-ahead plan_time, c-fill-target fill_target, c-delay-target
       delay_target, c-max-rate max_rate
	   The dynamic resync speed controller gets enabled with setting
	   plan_time to a positive value. It aims to fill the buffers along
	   the data path with either a constant amount of data fill_target, or
	   aims to have a constant delay time of delay_target along the path.
	   The controller has an upper bound of max_rate.

	   By plan_time the agility of the controller is configured. Higher
	   values yield for slower/lower responses of the controller to
	   deviation from the target value. It should be at least 5 times RTT.
	   For regular data paths a fill_target in the area of 4k to 100k is
	   appropriate. For a setup that contains drbd-proxy it is advisable
	   to use delay_target instead. Only when fill_target is set to 0 the
	   controller will use delay_target. 5 times RTT is a reasonable
	   starting value.  Max_rate should be set to the bandwidth available
	   between the DRBD-hosts and the machines hosting DRBD-proxy, or to
	   the available disk-bandwidth.

	   The default value of plan_time is 0, the default unit is 0.1
	   seconds.  Fill_target has 0 and sectors as default unit.
	   Delay_target has 1 (100ms) and 0.1 as default unit.	Max_rate has
	   10240 (100MiB/s) and KiB/s as default unit.

	   The dynamic resync speed controller and its settings are available
	   since DRBD 8.3.9.

       c-min-rate min_rate
	   A node that is primary and sync-source has to schedule application
	   IO requests and resync IO requests. The min_rate tells DRBD use
	   only up to min_rate for resync IO and to dedicate all other
	   available IO bandwidth to application requests.

	   Note: The value 0 has a special meaning. It disables the limitation
	   of resync IO completely, which might slow down application IO
	   considerably. Set it to a value of 1, if you prefer that resync IO
	   never slows down application IO.

	   Note: Although the name might suggest that it is a lower bound for
	   the dynamic resync speed controller, it is not. If the DRBD-proxy
	   buffer is full, the dynamic resync speed controller is free to
	   lower the resync speed down to 0, completely independent of the
	   c-min-rate setting.

	   Min_rate has 4096 (4MiB/s) and KiB/s as default unit.

       on-no-data-accessible ond-policy
	   This setting controls what happens to IO requests on a degraded,
	   disk less node (I.e. no data store is reachable). The available
	   policies are io-error and suspend-io.

	   If ond-policy is set to suspend-io you can either resume IO by
	   attaching/connecting the last lost data storage, or by the drbdadm
	   resume-io res command. The latter will result in IO errors of
	   course.

	   The default is io-error. This setting is available since DRBD
	   8.3.9.

       cpu-mask cpu-mask
	   Sets the cpu-affinity-mask for DRBD's kernel threads of this
	   device. The default value of cpu-mask is 0, which means that DRBD's
	   kernel threads should be spread over all CPUs of the machine. This
	   value must be given in hexadecimal notation. If it is too big it
	   will be truncated.

       pri-on-incon-degr cmd
	   This handler is called if the node is primary, degraded and if the
	   local copy of the data is inconsistent.

       pri-lost-after-sb cmd
	   The node is currently primary, but lost the after-split-brain auto
	   recovery procedure. As as consequence, it should be abandoned.

       pri-lost cmd
	   The node is currently primary, but DRBD's algorithm thinks that it
	   should become sync target. As a consequence it should give up its
	   primary role.

       fence-peer cmd
	   The handler is part of the fencing mechanism. This handler is
	   called in case the node needs to fence the peer's disk. It should
	   use other communication paths than DRBD's network link.

       local-io-error cmd
	   DRBD got an IO error from the local IO subsystem.

       initial-split-brain cmd
	   DRBD has connected and detected a split brain situation. This
	   handler can alert someone in all cases of split brain, not just
	   those that go unresolved.

       split-brain cmd
	   DRBD detected a split brain situation but remains unresolved.
	   Manual recovery is necessary. This handler should alert someone on
	   duty.

       before-resync-target cmd
	   DRBD calls this handler just before a resync begins on the node
	   that becomes resync target. It might be used to take a snapshot of
	   the backing block device.

       after-resync-target cmd
	   DRBD calls this handler just after a resync operation finished on
	   the node whose disk just became consistent after being inconsistent
	   for the duration of the resync. It might be used to remove a
	   snapshot of the backing device that was created by the
	   before-resync-target handler.

   Other Keywords
       include file-pattern
	   Include all files matching the wildcard pattern file-pattern. The
	   include statement is only allowed on the top level, i.e. it is not
	   allowed inside any section.

NOTES ON DATA INTEGRITY
       There are two independent methods in DRBD to ensure the integrity of
       the mirrored data. The online-verify mechanism and the
       data-integrity-alg of the network section.

       Both mechanisms might deliver false positives if the user of DRBD
       modifies the data which gets written to disk while the transfer goes
       on. This may happen for swap, or for certain append while global sync,
       or truncate/rewrite workloads, and not necessarily poses a problem for
       the integrity of the data. Usually when the initiator of the data
       transfer does this, it already knows that that data block will not be
       part of an on disk data structure, or will be resubmitted with correct
       data soon enough.

       The data-integrity-alg causes the receiving side to log an error about
       "Digest integrity check FAILED: Ns +x\n", where N is the sector offset,
       and x is the size of the request in bytes. It will then disconnect, and
       reconnect, thus causing a quick resync. If the sending side at the same
       time detected a modification, it warns about "Digest mismatch, buffer
       modified by upper layers during write: Ns +x\n", which shows that this
       was a false positive. The sending side may detect these buffer
       modifications immediately after the unmodified data has been copied to
       the tcp buffers, in which case the receiving side won't notice it.

       The most recent (2007) example of systematic corruption was an issue
       with the TCP offloading engine and the driver of a certain type of GBit
       NIC. The actual corruption happened on the DMA transfer from core
       memory to the card. Since the TCP checksum gets calculated on the card,
       this type of corruption stays undetected as long as you do not use
       either the online verify or the data-integrity-alg.

       We suggest to use the data-integrity-alg only during a pre-production
       phase due to its CPU costs. Further we suggest to do online verify runs
       regularly e.g. once a month during a low load period.

VERSION
       This document was revised for version 8.4.0 of the DRBD distribution.

AUTHOR
       Written by Philipp Reisner philipp.reisner@linbit.com and Lars
       Ellenberg lars.ellenberg@linbit.com.

REPORTING BUGS
       Report bugs to drbd-user@lists.linbit.com.

COPYRIGHT
       Copyright 2001-2008 LINBIT Information Technologies, Philipp Reisner,
       Lars Ellenberg. This is free software; see the source for copying
       conditions. There is NO warranty; not even for MERCHANTABILITY or
       FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
       drbd(8), drbddisk(8), drbdsetup(8), drbdmeta(8), drbdadm(8), DRBD
       User's Guide[1], DRBD web site[3]

NOTES
	1. DRBD User's Guide
	   http://www.drbd.org/users-guide/

	2. DRBD's online usage counter
	   http://usage.drbd.org

	3. DRBD web site
	   http://www.drbd.org/

DRBD 8.4.0			  6 May 2011			  DRBD.CONF(5)
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