FS(3) FS(3)
NAME
fs - file system devices
SYNOPSIS
bind -b #k /dev
/dev/fs
/dev/fs/ctl
/dev/fs/...
DESCRIPTION
The fs driver builds complex disk files out of simpler disk
files. Inspired by the Plan 9 file server kernel's configu-
ration strings, it provides device mirroring, partitioning,
interleaving, and catenation for disk-based services like
kfs(4) or venti(8).
The device is intended to be bound at /dev and contains a
directory named fs, which in turn contains a ctl file and
one file per configured device.
Most control messages each introduce a new device, here
named new. The file arguments are interpreted in the name
space of the writer.
cat new files...
The device new corresponds to the catenation of files.
inter new files...
The device new corresponds to the block interleaving of
files; an 8192-byte block size is assumed.
mirror new files...
The device new corresponds to a RAID-1-like mirroring
of files. Writes to new are handled by sequentially
writing the same data to the files from right to left
(the reverse of the order in the control message). A
failed write causes an eventual error return but does
not prevent the rest of the writes to the other devices
of the mirror set. 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.
clear
Page 1 Plan 9 (printed 5/19/12)
FS(3) FS(3)
Discard all fs device definitions.
If the variable fsconfig is set in plan9.ini(8) then fs 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/fs/m0; similarly, mirror /dev/sdC1/data and
/dev/sdD1/data as /dev/fs/m1:
echo mirror m0 /dev/sdC0/data /dev/sdD0/data >/dev/fs/ctl
echo mirror m1 /dev/sdC1/data /dev/sdD1/data >/dev/fs/ctl
Interleave the two mirrored disks to create /dev/fs/data:
echo inter data /dev/fs/m0 /dev/fs/m1 >/dev/fs/ctl
Run kfs(4) on the interleaved device:
disk/kfs -f /dev/fs/data
Save the configuration:
cp /dev/fs/ctl /dev/fd0disk
To load the configuration automatically at boot time, add
this to plan9.ini:
fsconfig=/dev/fd0disk
SEE ALSO
read in cat(1), dd(1), sd(3), kfs(4), fs(8), plan9.ini(8),
prep(8), venti(8)
SOURCE
/sys/src/9/port/devfs.c
BUGS
Mirrors are RAID-like but not RAID. There is no fancy
recovery mechanism and no automatic initial copying from a
master drive to its mirror drives.
Each write system call on ctl may transmit at most one com-
mand.
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