Re: split RAID1 during backups?

[Brad Campbell <brad@wasp.net.au>]

Jeff Breidenbach wrote:

> So - I'm thinking of the following backup scenario.  First, remount
> /dev/md0 readonly just to be safe. Then mount the two component
> paritions (sdc1, sdd1) readonly. Tell the webserver to work from one
> component partition, and tell the backup process to work from the
> other component partition. Once the backup is complete, point the
> webserver back at /dev/md0, unmount the component partitions, then
> switch read-write mode back on.

Why not do something like this ?

mount -o remount,ro /dev/md0 /web
mdadm --fail /dev/md0 /dev/sdd1
mdadm --remove /dev/md0 /dev/sdd1
mount -o ro /dev/sdd1 /target

<do backup here>

umount /target
mdadm -add /dev/md0 /dev/sdd1
mount -o remount,rw /dev/md0 /web

That way the web server continues to run from the md..
However you will endure a rebuild on md0 when you re-add the disk, but given everything is mounted 
read-only, you should not practically be doing anything and if you fail a disk during the rebuild 
the other disk will still be intact.

I second jurriaan's vote for rsync also, but I would be inclined just to let it loose on the whole 
disk rather than break it up into parts.. but then I have heaps of ram too..

Regards,
Brad
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