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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 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.



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
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 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.





DS(3
)
Rev:  Tue Mar 31 02:42:38 GMT 2015