presto man page on DigitalUNIX

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presto(8)							     presto(8)

NAME
       presto - Controls and monitors the Prestoserve file system accelerator

SYNOPSIS
       /usr/sbin/presto [options]

OPTIONS
       Disables	 Prestoserve  and  writes  the	Prestoserve  cache data to the
       intended disks. If no file systems are specified, all accelerated  file
       systems are disabled, and the Prestoserve state is set to DOWN.

	      The  filesystem  parameter  can be used to disable specific file
	      systems. You specify filesystem as a directory mount point  (for
	      example,	/usr).	If no file systems are specified, all acceler‐
	      ated file systems are disabled, and the Prestoserve state is set
	      to DOWN.

	      Do  not  specify	a block device because some functional subsys‐
	      tems, such as the Advanced File System  (AdvFS),	can  map  more
	      than one block device to a mount point.

	      This option does not reset Prestoserve statistics.

	      The -d option takes effect before the -u or -R options.  Similar
	      to the -d option, but sets the Prestoserve state to DOWN only if
	      the  specified  directory	 is the root of a mounted file system.
	      Otherwise, the following message is displayed: presto: directory
	      is not a file system root Flushes (writes) the Prestoserve cache
	      data to the intended disks, but leaves the cache data intact.

	      If the option is used and the Prestoserve state is UP, then  the
	      cache  data  is  written	to  the	 intended disks, and the state
	      remains UP. If the Prestoserve state is DOWN, then there	is  no
	      data  to write to the disks, and the state remains DOWN.	If the
	      state is ERROR, then as much of the cache data  as  possible  is
	      written to the intended disks.

	      Note  that  unlike  the  -R  option, the data in the Prestoserve
	      cache remains after it is written to the intended disks.	 Lists
	      the  accelerated file systems and their mount points in a format
	      similar to the mount command.  This  option  can	be  used  with
	      either  NFS  client  or server machines.	Lists all mounted file
	      systems and their mount points that have been accelerated.   Any
	      unusual  Prestoserve  state for a file system is displayed after
	      the mount point. The unusual states include: Instead of directly
	      accessing	 the  nonvolatile  memory,  the	 file  system's device
	      receives the Prestoserve data  only  after  the  data  is	 first
	      copied  to main memory.  Prestoserve acceleration is not enabled
	      on the file system.  An error occurred using  the	 file  system,
	      and  the	Prestoserve cache data has still not been written suc‐
	      cessfully to the intended disks.	Displays Prestoserve  informa‐
	      tion.   The  information includes the current Prestoserve state;
	      the statistics for write, read, and total operations;  and  bat‐
	      tery  status.   For  example:  # /usr/sbin/presto -p dirty = 52,
	      clean = 7, inval = 903, active = 2
		     count hit rate clean hits dirty hits  allocations	passes
	      write:  1516	65%	     0	      989	  511	  15
	       read:	  8	   0%	       0	  0	      0	     8
	      total:  1524	65%	     0	      989	   511	    23
	      state  =	UP, size = 0x7e000 bytes statistics interval: 00:00:13
	      (13 seconds) write cache efficiency: 66% All batteries are ok

	      The current Prestoserve statistics account for  all  Prestoserve
	      buffers.	 A  dirty  buffer contains a disk block image that has
	      not been written to disk.	 A clean buffer contains a valid  disk
	      block image that has been written to disk.  An inval buffer does
	      not presently contain a disk block image.	 An active  buffer  is
	      currently	 in transition to disk, meaning that a write operation
	      has started but has not completed on that buffer.

	      For each Prestoserve cache read or write operation,  Prestoserve
	      increments  a  counter, as follows: The clean hits counter shows
	      the number of hits (block matches) on the	 clean	buffers.   The
	      dirty  hits  counter  shows the number of hits on the dirty buf‐
	      fers. Each dirty hit on a write represents a physical disk write
	      that  was	 avoided  entirely, while a hit on a read represents a
	      physical disk read that was avoided.   The  allocations  counter
	      shows  the  number  of  new buffers that had to be allocated for
	      disk block images.  The passes counter shows the number  of  I/O
	      operations  that	Prestoserve passed directly to the real device
	      driver.

	      In addition, for each Prestoserve cache read or write operation,
	      the  presto  -p  command displays the count, which is the sum of
	      the four counters explained previously; the hit rate percentage,
	      which  is	 the  ratio  of clean hits and dirty hits to the total
	      count and which indicates the effectiveness of  the  Prestoserve
	      cache;  and the write cache efficiency percentage, which is com‐
	      puted from the ratio of write dirty hits to the number of writes
	      copied into the Prestoserve cache.

	      The  presto  -p  command	also  displays	information  about the
	      Prestoserve battery state.  The  command	displays  the  battery
	      state as ok, low, or disabled.

	      Some  processors support chargeable batteries and use self tests
	      to determine if a battery needs charging. If you use the	presto
	      -p  command on a machine that supports chargeable batteries, the
	      battery state can also be in self test or is charging. Note that
	      if  you use the dxpresto command, batteries that are being self-
	      tested or charged will be displayed as disabled.	Writes as much
	      of  the Prestoserve cache data as possible to disk, discards the
	      data it could not write, purges all the Prestoserve buffers, and
	      sets the Prestoserve state to DOWN.

	      Unlike  the  -d  option,	the -R option discards the Prestoserve
	      cache data that could not be written to disk and resets the sta‐
	      tistics information. The option is useful when Prestoserve cache
	      data is not needed or if you cannot get Prestoserve out  of  the
	      ERROR state.

					  Caution

	      Take  care  when	using  the  -R	option,	 because  it  destroys
	      Prestoserve cache data.

	      The -R option takes effect before the -u option.	Sets the  size
	      of  the Prestoserve cache to size bytes.	The size can be speci‐
	      fied using the decimal or hexadecimal conventions.  For example,
	      both 262144 and 0x40000 represent 256 Kbytes.

	      If  the  -s  option is used and the current Prestoserve state is
	      UP, the state is set to DOWN, the Prestoserve cache is  resized,
	      and the state is set to UP.

	      You  may	want to use the -s option to determine how Prestoserve
	      performs with a reduced amount of nonvolatile memory.  Note that
	      the  size	 of  the  Prestoserve  cache cannot be larger than the
	      default maximum size or smaller than the default	minimum	 size.
	      If  you  specify	a size that is larger than the default maximum
	      size, the default maximum size is used.  If you specify  a  size
	      that is smaller than the default minimum size, the default mini‐
	      mum size is used.	 Sets Prestoserve state	 to  UP,  and  enables
	      acceleration.

	      If  no  file systems are specified, all local writable file sys‐
	      tems that are mounted will have Prestoserve enabled.  File  sys‐
	      tems that are presently accelerated will remain accelerated.

	      The  filesystem  parameter  can  be used to enable specific file
	      systems.	You specify filesystem as a directory mount point (for
	      example, /usr).

	      Do  not  specify	a block device because some functional subsys‐
	      tems, such as the Advanced File System  (AdvFS),	can  map  more
	      than one block device to a mount point.

	      If  Prestoserve  state  was ERROR, Prestoserve attempts to write
	      any blocks that are in the cache to disk to ensure that the pre‐
	      vious  error  condition  has  been corrected.  Similar to the -u
	      option, but sets the Prestoserve state to UP only if the	speci‐
	      fied  directory is the root of a mounted file system. Otherwise,
	      the following message is displayed: presto: directory is	not  a
	      file  system  root  Specifies  verbose mode.  This option prints
	      extra information to standard output.  The  information  can  be
	      used for debugging purposes.

DESCRIPTION
       The  presto  command  allows  you  to  accelerate  file systems, obtain
       Prestoserve status, and administer Prestoserve.

       If invoked with no  options,  presto  displays  the  Prestoserve	 state
       (either	UP, DOWN, or ERROR), the number of bytes of nonvolatile memory
       the Prestoserve cache is using, how long the cache  has	been  enabled,
       the write cache efficiency, and the state of the backup battery or bat‐
       teries.

       When the Prestoserve state is UP, Prestoserve improves I/O  performance
       to  accelerated	file  systems by caching synchronous disk write opera‐
       tions to nonvolatile memory.

       When the Prestoserve state is DOWN, all I/O requests are passed to  the
       appropriate disks.

       If  it detects a disk error during a write back, Prestoserve enters the
       ERROR state and disables itself.	  However,  Prestoserve	 continues  to
       maintain the integrity of cached data.  Some possible disk error condi‐
       tions are:  the disk drive is write protected  or  off  line,  a	 cable
       problem exists, or a bad disk block exists.

       Also,  if  there is insufficient backup battery power, Prestoserve will
       enter the ERROR state.

FILES
       Generic Prestoserve control device.

SEE ALSO
       Commands: prestoctl_svc(8), prestosetup(8), dxpresto(8X)

       Files: prestotab(4)

       Networking: presto(7)

       Guide to Prestoserve

								     presto(8)
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