DS(3) Library Functions Manual DS(3)

ds - compound device subsystems

bind -b #k /dev
/dev/ds
/dev/ds/ctl
/dev/ds/...

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 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.

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.
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.
The device new corresponds to the block interleaving of files; an 8192-byte block size is assumed.
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.

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

dossrv (4)

/os/port/devds.c

Should be able to select block size for interleaved devices.