zfs discuss - May 2010 - Daily snapshots as replacement for incremental backups

Hello,
I have a situation where a zfs file server holding lots of graphic files cannot
be backed up daily with a full backup.
My idea was initially to run a full backup on Sunday through the lto library on
more dedicated tapes, then have an incremental backup run on daily tapes.
Brainstorming on this, led me to the idea that I could actually stop thinking
about incremental backups (that may always lead me to unsafe backups anyway for
some unlucky reason) and substitute the idea with daily snapshots.
Actually, the full disaster ricovery is on the Sunday full backups (that can be
safely taken away on Monday), while the daily solution would be just a safe
place for daily errors by users (people who delete files by mistake, for
example).
This can be done simply running a snapshot per day during the night.
My idea is to have cron to rotate snapshots during working days, so that I
always have Mon,Tue,Wen,Thu,Fri,Sat snapshots, and have the cron shell delete
the oldest (actually, if I have to run a Mon snapshot, I will delete the old Mon
snapshots, this should run the cycle).
My questions are:
- is this a good and common solution?
- is there any zfs performance degradation caused by creating and deleting
snapshots on a daily basis, maybe fragmenting the file system?

Thanx for any suggestion
Gabriele.
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This message posted from opensolaris.org

Gabriele Bulfon wrote:
> Hello,
> I have a situation where a zfs file server holding lots of graphic files
cannot be backed up daily with a full backup.
> My idea was initially to run a full backup on Sunday through the lto
library on more dedicated tapes, then have an incremental backup run on daily
tapes.
> Brainstorming on this, led me to the idea that I could actually stop
thinking about incremental backups (that may always lead me to unsafe backups
anyway for some unlucky reason) and substitute the idea with daily snapshots.
> Actually, the full disaster ricovery is on the Sunday full backups (that
can be safely taken away on Monday), while the daily solution would be just a
safe place for daily errors by users (people who delete files by mistake, for
example).
> This can be done simply running a snapshot per day during the night.
> My idea is to have cron to rotate snapshots during working days, so that I
always have Mon,Tue,Wen,Thu,Fri,Sat snapshots, and have the cron shell delete
the oldest (actually, if I have to run a Mon snapshot, I will delete the old Mon
snapshots, this should run the cycle).
> My questions are:
> - is this a good and common solution?
>   
Yes, though of course you realize that snapshots are not a 
disaster-recovery mechanism.  They''re not really backups, either, in
the
sense that they provide no security against larger-scale failures.
> - is there any zfs performance degradation caused by creating and deleting
snapshots on a daily basis, maybe fragmenting the file system?
>   
No.  Well, that''s not strictly true, but you won''t run into
any issues
with snapshots until you have a very large number of them 
simultaneously. 1000s, or more.  Snapshots don''t fragment the file 
system any more than deleting files does.  Taking snapshots is 
instantaneous, while deleting a snapshot can vary in time from virtually 
instantaneous to taking several hours (or more), if you have dedup 
turned on and have a large amount of data (and, don''t have sufficient 
L2ARC or RAM to hold the dedup table).  In the latter case, it will 
impact performance, as the entire pool has to be scanned to allow for 
proper deletion of the deduped snapshot (i.e. it has to scan the entire 
pool to figure out which data is deduped, and what can be safely deleted).


> Thanx for any suggestion
> Gabriele.
>   

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