Re: Rotating RAID 1

[Pavel Hofman <pavel.hofman@ivitera.com>]

Dne 15.8.2011 21:56, Jérôme Poulin napsal(a):
> Good evening,
> 
> I'm currently working on a project in which I use md-raid RAID1 with
> Bitmap to "clone" my data from one disk to another and I would like to
> know if this could cause corruption:
> 
> The system has 2 SATA ports which are hotplug capable.
> I created 2 partitions, 1 system (2GB), 1 data (1TB+).
> I created to RAID1 using:
> mdadm --create /dev/md0 --raid-devices=2 --bitmap=internal
> --bitmap-chunk=4096 --metadata=1.0 /dev/sd[ab]1
> mdadm --create /dev/md1 --raid-devices=2 --bitmap=internal
> --bitmap-chunk=65536 --metadata=1.0 /dev/sd[ab]2
> Forced sync_parallel on the system disk to be sure it rebuild first.
> Formatted system ext3 and data ext4.
> Both mounted using data=writeback.
> 
> This system doesn't contain critical data but it contains backups on
> the data partition. Once the data is in sync, I removed a disk and let
> udev fail and remove the disk from the array, this is ArchLinux and
> udev is set to mount the array using the incremental option, I added
> --run to make sure it mounts even when a disk is missing. As of now,
> eveything works as expected.
> 
> Then what is different about a standard RAID1, I removed sdb and
> replaced it with a brand new disk, copied the partition template from
> the other one and added the new disk using mdadm -a on both arrays, it
> synced and works, then swapping the other disk back only rebuilds
> according to the bitmap, however sometimes it appears to make a full
> rebuild which is alright. However once, after a day of modifications
> and weeks after setting-up this RAID, at least 100 GB, it took seconds
> to rebuild and days later it appeared to have encountered corruption,
> the kernel complained about bad extents and fsck found errors in one
> of the file I know it had modified that day.

Does your scenario involve using two "external" drives, being swapped
each time? I am using such setup, but in order to gain the bitmap
performance effects, I have to run two mirrored RAID1s, i.e. two
bitmaps, each for its corresponding external disk. This setup has been
working OK for a few years now.

Best regards,

Pavel.
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html