zfs discuss - Mar 2010 - Thoughts pls. : Create 3 way rpool mirror and shelve one mirror as a backup

Hi guys,
   On my home server (2009.6) I have a 2 HDD''s in a mirrored rpool.

I just added a 3rd to the mirror and made all disks bootable (ie. installgrub on
the mirror disks).

My though is this, I remove the 3rd mirror disk and offsite it as a backup.

That way if I mess up the rpool, I can get back the offsite HDD, boot from it
and re-mirror this to the other 2 HDD''s and I am back in business.

I plan to leave the 3rd mirror device in the rpool (just no HDD loaded so it
will show as degraded all the time). On a monthly basis, I''ll
physically insert the 3rd HDD and get it to resilver and then remove the 3rd hdd
offsite again - ie. refresh the backup.

Anyone see any flaws in this plan?
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This message posted from opensolaris.org

On Mar 6, 2010, at 5:38 PM, tomwaters wrote:
> Hi guys,
>   On my home server (2009.6) I have a 2 HDD''s in a mirrored rpool.
> 
> I just added a 3rd to the mirror and made all disks bootable (ie.
installgrub on the mirror disks).
> 
> My though is this, I remove the 3rd mirror disk and offsite it as a backup.
> 
> That way if I mess up the rpool, I can get back the offsite HDD, boot from
it and re-mirror this to the other 2 HDD''s and I am back in business.
> 
> I plan to leave the 3rd mirror device in the rpool (just no HDD loaded so
it will show as degraded all the time). On a monthly basis, I''ll
physically insert the 3rd HDD and get it to resilver and then remove the 3rd hdd
offsite again - ie. refresh the backup.
> 
> Anyone see any flaws in this plan?

To do this either:
	1. upgrade to a later version where the "zpool split" command is
available
	2. zfs send/receive to the disk to be stored offsite

IMHO, splitting mirros for backups is a waste of time, but it is a popular way
of
backup for non-ZFS file systems.
 -- richard

ZFS storage and performance consulting at http://www.RichardElling.com
ZFS training on deduplication, NexentaStor, and NAS performance
http://nexenta-atlanta.eventbrite.com (March 16-18, 2010)

On Sat, 6 Mar 2010, Richard Elling wrote:
> On Mar 6, 2010, at 5:38 PM, tomwaters wrote:
>
>> My though is this, I remove the 3rd mirror disk and offsite it as a
backup.
>
> To do this either:
> 	1. upgrade to a later version where the "zpool split" command is
available
> 	2. zfs send/receive to the disk to be stored offsite
Note that zpool split does not support a re-join.  Once the split is 
split, it''s split for good.  To use it as an off-site backup,
it''d be
better to do a zpool offline instead, and then pull the disk.

Hi tomwater! 

I think this is a great idea and may be the only reasonable way to backup tera
bytes of data with low cost disks. And the idea is quite popular, just google
*split mirror backup* and get lots of results. I also intend to use ZFS like
this.
- 3 way mirror
- 1 disk offsite at all times (2 disks when rotating to a newer backup date)
- ZFS snapshots for history
- ZFS scrub to verify each backup disk just before offlining it

Good Luck 
Ludwig
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This message posted from opensolaris.org

Thanks guys,
     It''s all working perfectly so far....and very easy too.

Given that my boot disks (consumer laptop drives) cost only ~$60AUD each,
it''s a cheap way to maintain high availability and backup.

ZFS does not seem to mind having one of the 3 offline so I''d recomend
this to others looking for a simple offline backup solution (just remember to
install grub on the "spare" to make it bootable)...but you''d
test your backups anyway before you send them offsite...wouldn''t you :)
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