swapping RAID1 disk and hot-swap disk for restore image test

Gernot Hassenpflug aikishugyo at gmail.com
Fri Mar 19 04:11:03 CDT 2010

On Fri, Mar 19, 2010 at 5:33 PM,  <Jens_Heinz at dell.com> wrote:
> It should work this way:

Dear Jens,
Thank you for the judicious and informative reply.

> 1. goto RAID BIOS
> 2. offline both RAID1 HDDs
> 3. create a RAID0 in hotspare drive
> 4. change 'bootable VD'
> 5. do your restore tests
> To go back to your original configuration I would recommend to just
> online one of your both RAID1 HDDs and rebuild the other if all is fine.

OK, I can understand the above steps, and if this works I will be
happy. Although I must admit I have not onlined a partial array and
rebuilt the rest before. A major worry I had is that once the RAID1 is
reattached after the test, that I will be forced to "initialize" it,
which means deleting data. The manual says I can force a consistency
check if I do not choose to initialize, but I did not trust the manual
to be necessarily applicable for my circumstances.

> This approach has two advantages, avoid issue when forcing 2x HDDs
> online at once and you still have your data available on your 2nd HDD if
> something goes wrong with 1st one.

OK, I understand the first part. But not very well! Can I ask for a
bit more clarity? I know the 2 disks are synchronized, so I would like
to put them both back online.
If I put only one online (still in the controller) and there is
something wrong with the data, a rebuild will overwrite data on the
other drive with bad data, I think. I don't have the experience to
know better, but it seems like not a worthwhile trade-off. I'd love to
hear a bit more...

> One thing you need to consider in your scenario, if you're using
> /dev/sdX device numbering. Your RAID1 will usually be /dev/sda (even if
> you failed/offlined it) and your RAID0 will be /dev/sdb. This might
> affect GRUB, mount points etc. from your restored image.

Yes, that is indeed an issue. In fact, for me, sda is the MD1000
backup array and sdb is the RAID1 at this time. Presumably RAID0 will
then be sdc. The backup image will be a separate ISO image from the
clonezilla backup software ISO, so I can select the device to restore
to. A combined Clonezilla/restore data image would automatically
restore to a pre-defined disk, and that can be a hassle under the
above circumstances.

I'm delighted to hear that in theory there is no problem with doing this job.
Many thanks,
Gernot Hassenpflug

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