DS(3) DS(3)
NAME
ds - 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 configu-
ration strings, it provides device mirroring, partitioning,
interleaving, and catenation for block-oriented file sys-
tems.
It serves a two-level directory. The top level contains a
single directory ds, which contains a control file ctl and
one file per configured 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 writ-
ing 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 offset 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
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DS(3) DS(3)
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 ALSO
dossrv(4)
SOURCE
/os/port/devds.c
BUGS
Should be able to select block size for interleaved devices.
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