software raid on removable drives for backups

[A. Khattri]

On Tue, 1 Feb 2005, Jason Joines wrote:

>     I'd like to use sets of big removable drives as backup media.
> Ideally, a 3 disk RAID-5 set would be built and a weekly backup written
> to it.  Then, another 3 disk set would be stuck in .....  Only problem
> is I would need to be able to non-destructively reinsert the first set
> to get data off of it if a restore was needed.  Can software raid do this?

I haven't tried software RAID for RAID-5 but I am using it for RAID-1 on a
few servers (where I couldn't afford a RAID card) with SCSI disks.

Basically, the kernel will mark a drive as bad when it fails and take it
out of the group. If you have raidtools installed you have commands to
take drives and and out of the group and to rebuild a replaced drive. To
check on the arrays you can cat /proc/mdstat and get something like this:

Personalities : [linear] [raid0] [raid1] [raid5] [multipath] [raid6]
[raid10]
md1 : active raid1 sdc3[1] sda3[0]
      104320 blocks [2/2] [UU]

md3 : active raid1 sdc5[1] sda5[0]
      4008064 blocks [2/2] [UU]

md4 : active raid1 sdc6[1] sda6[0]
      12747456 blocks [2/2] [UU]

md2 : active raid1 sdd1[1] sdb1[0]
      35559744 blocks [2/2] [UU]

md0 : active raid1 sdc1[1] sda1[0]
      56128 blocks [2/2] [UU]

unused devices: <none>


(Ive got pairs of drives spread across two SCSI channels for better
performance, this is why sdc3 is paired with sda3, etc).


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