[linux-lvm] Using LVM snapshots for hourly backups
Jonathan E Brassow
jbrassow at redhat.com
Wed Oct 11 13:25:49 UTC 2006
I think everyone feels the same way about the current snapshot
implementation, and there is growing momentum for change. See
"[dm-devel] [RFC] DM Snapshot scalability - Common snap store approach"
(Oct 9th on dm-devel).
Certainly, any changes will take a while though.
On Oct 10, 2006, at 3:00 PM, Anthony Wright wrote:
> I'm trying to work out if there's a way to use LVM snapshots to create
> hourly backups of my data. I realise that this doesn't protect me
> against disk/machine failure, but it would really handy in cases where
> I want easy access to historical files, e.g where I accidentally
> change/delete a file or I want to compare historical files/directories
> to the current versions to see what's been changed.
> I thought a really simple and ingeneous approach would be to use LVM
> snapshots so that each hour I make a snapshot, and remove the snapshot
> from 24 hours ago, thus having a rolling hourly backup. However when I
> tried this I ended up with 24 snapshots of the original volume which
> means a single change to the original volume causes each snapshot to
> do a Copy on Write of the changed block, so if I change one block on
> the original volume the snapshots create 24 copies of the original
> volume which isn't very good for disk performance or disk usage!!
> What I'd really want is to daisy-chain the snapshots so that
> snapshot-3hours is a snapshot of snapshot-2hours, which is a snapshot
> of snapshot-1hour, which is a snapshot of the original volume, thus if
> a block in the original volume changes only snapshot-1hour is changed
> and once a snapshot is older than an hour it cannot change any more.
> I notice that you can't make snapshots of snapshots, so I suspect what
> I'm looking for isn't possible, but I thought I check and if it isn't
> possible suggest it as a really useful feature for the future. Your
> thoughts/comments would be welcome.
> Tony Wright.
> linux-lvm mailing list
> linux-lvm at redhat.com
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
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