[linux-lvm] Using LVM Mirroring to obtain a usable backup

[Stuart D. Gathman]

On Thu, 17 Sep 2009, Brian J. Murrell wrote:

> > The rollback also needs to be quick.
> 
> Which a snapshot will achieve.
> 
> > A snapshot with dd does the "instant" backup part ok, but rollback
> > requires 5-6 hours to copy the snapsnot to a normal LV.
> 
> Why would you copy the snapshot anywhere?  If you decided you needed a
> roll-back, you boot from the snapshot of the root filesystem and have
> the /etc/fstab in that snapshot mount any snapshots of other filesystems
> he might have made.  Personally, I keep separate /, /usr, and /var and
> so snapshot them all before an upgrade and fix up the /etc/fstab in the
> snapshot-of-/ to mount the /usr and /var snapshots (rather than the
> origins).

1) Eventually you still need to copy the snapshot to a normal LV to get 
your performance back - and that will involve 5-6 hours downtime.

2) (minor, but important) Another FAQ is "exactly how big do I need to make my
snapshot so that it is guaranteed never to overflow".

> > I always build my VGs on md* devices.
> 
> I typically have not.  I typically don't mirror anything except my
> backup volume, which fully (as in bare metal restore able) backs up
> every filesystem I have in my network.  For that reason I feel that
> mirroring the disks in all the machines is overkill.

Those with money to burn seem to favor SANs. (And cloning a PV with
a SAN and importclone is an easy solution to the OP problem - if only they had
a SAN.) I'm part of the Po' Fo'k contingent.

-- 
	      Stuart D. Gathman <stuart at bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
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