DS(3)DS(3)NAMEds - compound device subsystems
SYNOPSIS
bind -b #k /dev
/dev/ds
/dev/ds/ctl
/dev/ds/...
DESCRIPTION
Ds builds complex block storage subsystems out of simpler ones.
Inspired by the Plan 9 file server kernel's configuration strings, it
provides device mirroring, partitioning, interleaving, and catenation
for block-oriented file systems.
It serves a two-level directory. The top level contains a single
directory ds, which contains a control file ctl and one file per con‐
figured device.
The control messages each introduce a new device, here named new. The
file arguments are interpreted in the name space of the writer.
mirror new files...
The device new corresponds to a RAID 1 mirroring of files.
Writes to new are handled by sequentially writing to the files
from right to left (the reverse of of the order in the control
message). If any write fails, the write is aborted. Reads from
new are handled by sequentially reading from the files from left
to right until one succeeds. The length of the mirror device is
the minimum of the lengths of the files.
part new file offset length
The device new corresponds to the length bytes starting at off‐
set in file. If offset+length reaches past the end of file,
length is silently reduced to fit.
inter new files...
The device new corresponds to the block interleaving of files;
an 8192-byte block size is assumed.
cat name files...
The device new corresponds to the catenation of files.
If the variable fsconfig is set in plan9.ini(8) then ds will read its
configuration from the file $fsconfig on the first attach. This is
useful when the machine boots from a local file server that uses fs.
EXAMPLE
Mirror the two disks /dev/sdC0/data and /dev/sdD0/data as /dev/ds/m0;
similarly, mirror /dev/sdC1/data and /dev/sdD1/data as /dev/ds/m1:
echo mirror m0 /dev/sdC0/data /dev/sdD0/data >/dev/ds/ctl
echo mirror m1 /dev/sdC1/data /dev/sdD1/data >/dev/ds/ctl
Interleave the two mirrored disks to create /dev/ds/data:
echo inter data /dev/ds/m0 /dev/ds/m1 >/dev/ds/ctl
Run kfs(4) on the interleaved device:
disk/kfs -f /dev/ds/data
Save the configuration:
cp /dev/ds/ctl /dev/fd0disk
To load the configuration automatically at boot time, add this
to plan9.ini:
fsconfig=/dev/fd0disk
SEE ALSOdossrv(4)SOURCE
/os/port/devds.c
BUGS
Should be able to select block size for interleaved devices.
DS(3)
