December 2002
Intermediate to advanced
260 pages
9h 18m
English
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RAID-1 (Mirroring)
Setting up a mirror is slightly different from using linear mode or RAID-0. We already know that mirroring replicates data across all member disks. This allows a RAID-1 to continue functioning even if a disk fails. The simplest RAID-1 configuration must contain at least two member disks. In this example, /dev/sdb1 and /dev/sdc1 are member disks of the RAID-1 at /dev/md0:
# A RAID-1 with two member disks raiddev /dev/md0 raid-level 1 nr-raid-disks 2 chunk-size 64 device /dev/sdb1 raid-disk 0 device /dev/sdc1 raid-disk 1
chunk-size has no effect on RAID-1 because no
disk striping is involved. But chunk-size is still
required as a placeholder. Note also that the
persistent-superblock isn’t needed for RAID-1. Use
mkraid to create this array:
#mkraid/dev/md0handling MD device /dev/md0 analyzing super-block disk 0: /dev/sdb1, 17920476kB, raid superblock at 17920384kB disk 1: /dev/sdc1, 17920476kB, raid superblock at 17920384kB
Or, using mdadm:
# mdadm -Cv -l1 -n2 /dev/md0 /dev/sd{b,c}1
mdadm: array /dev/md0 started.Whenever a new mirror is created, resynchronization occurs:
# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid5]
read_ahead 1024 sectors
md0 : active raid1 sdc1[1] sdb1[0]
17920384 blocks [2/2] [UU]
[= = = = = = = =>............] resync = 40.2% (7212864/17920384)
finish=6.4min speed=27652K/sec
unused devices: <none>Now /proc/mdstat reports information about the array and also includes information about the resynchronization process. Resynchronization ...
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