On Tue, 2010-03-02 at 22:50 +1300, Daniel Reurich wrote: > Hi Guys. > > I'm considering implementing a rotating offsite backup solution using > raid 1. This solution uses 1 or more internal drives and 2 external > e-sata harddrives. The raid setup would be a whole disk partitionable > raid1 volume. > > The idea is that by swapping the external drives, I can have a > boot-able ready to run offsite backup of the machine, as well as > redundancy on the machine itself. Backups of the important data would > be replicated via an incremental daily backup process onto the raid > volume itself. > > The part that concerns me is how to get a clean removal of the drive > being swapped out, and how will the raid handle having a stale drive > inserted/re-added. > > I have been considering a couple of ways to handle this: > > 1) Power the machine down to swap the drives. This has the advantage > that the backup is always in a clean bootable state with filesystem > consistency pretty much guaranteed. > > 2) Use mdadm to fail and remove the drives, and then re-add the newly > attached stale drive. (Perhaps a udev rule could be made handle the > re-add). The disadvantage is this will potentially leave the backup with an inconsistent filesystem and possibly have some corrupted files unless there is a way to programmatically queisce all write filesystem write activity and sync the disk before the removal. > It will also mark the drive as failed and require mdadm --re-add to > insert the spare drive. It's advantage is that the machine > doesn't need to be turned off. > > 3) Hot pull the drive e-sata cable, then power down the drive. This is > likely to leave the filesystems in really nasty state if there just > happens to be a write going on at the time. Actually scrap 3 as on re-reading it goes against all sensibility. > > My preference is for option 2 as option 1 may not always be feasible due > to the downtime, but I'm wondering about how best to handle the re-add, > as I suspect that the metadata on the failed then removed drive, would > make it more difficult to re-add the drive into the array. > > If option 1 was used (cold swap), how would md handle assembly with the > stale but not failed member disk? Would it simply force a resync, or > would it fail the disk and require manual intervention to re-add it. > > Any thoughts on my hair brained scheme would be appreciated. > > Daniel Reurich. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
