[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.
> Thanks,
> Tony Wright.
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