ref: 9ca327dd06c30341d984bff84727ea451b428db7
dir: /man/3/ds/
.TH DS 3 .SH NAME ds \- compound device subsystems .SH SYNOPSIS .nf .B bind -b #k /dev .B /dev/ds .B /dev/ds/ctl .B /dev/ds/... .fi .SH DESCRIPTION .I 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. .PP It serves a two-level directory. The top level contains a single directory .BR ds , which contains a control file .B ctl and one file per configured device. .PP The control messages each introduce a new device, here named .IR new . The .I file arguments are interpreted in the name space of the writer. .TP .BI mirror " new files" \fR... The device .I new corresponds to a RAID 1 mirroring of .IR files . Writes to .BI new are handled by sequentially writing to the .I 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 .BI new are handled by sequentially reading from the .I files from left to right until one succeeds. The length of the mirror device is the minimum of the lengths of the .IR files . .TP .BI part " new file offset length" The device .I new corresponds to the .I length bytes starting at .I offset in .IR file . If .IR offset + length reaches past the end of .IR file , .I length is silently reduced to fit. .TP .BI inter " new files" \fR... The device .I new corresponds to the block interleaving of .IR files ; an 8192-byte block size is assumed. .TP .BI cat " name files" \fR... The device .I new corresponds to the catenation of .IR files . .PD .LP If the variable .B fsconfig is set in .IR plan9.ini (8) then .I ds will read its configuration from the file .B $fsconfig on the first attach. This is useful when the machine boots from a local file server that uses .IR fs . .SH EXAMPLE Mirror the two disks .B /dev/sdC0/data and .B /dev/sdD0/data as .BR /dev/ds/m0 ; similarly, mirror .B /dev/sdC1/data and .B /dev/sdD1/data as .BR /dev/ds/m1 : .IP .EX echo mirror m0 /dev/sdC0/data /dev/sdD0/data >/dev/ds/ctl echo mirror m1 /dev/sdC1/data /dev/sdD1/data >/dev/ds/ctl .EE .LP Interleave the two mirrored disks to create .BR /dev/ds/data : .IP .EX echo inter data /dev/ds/m0 /dev/ds/m1 >/dev/ds/ctl .EE .LP Run .IR kfs (4) on the interleaved device: .IP .EX disk/kfs -f /dev/ds/data .EE .LP Save the configuration: .IP .EX cp /dev/ds/ctl /dev/fd0disk .EE To load the configuration automatically at boot time, add this to .IR plan9.ini : .IP .EX fsconfig=/dev/fd0disk .EE .SH "SEE ALSO" .IR dossrv (4) .SH SOURCE .B /os/port/devds.c .SH BUGS Should be able to select block size for interleaved devices.