Re: db and storage snapshot - may be a little OFF-TOPIC

From: Ryan January <rjjanuary_at_multiservice.com>
Date: Fri, 28 Jun 2013 11:05:11 -0500
Message-ID: <51CDB437.9060102_at_multiservice.com>

It may also benefit to double check exactly how the snapshots are occurring and how space is allocated. I'm not familiar with that particular storage, however I've learned to not assume an even block-for-block allocation for snapshot changes.

At the device level some systems use "extents" for lack of a better term. As an example; some Dell equalogic arrays break large files down into 1MB chunks. If a single block of that 1MB chunk changes, a full 1MB of space is allocated to the snapshot. Assuming an equal distribution of changes and an 8k block size it would theoretically only require a change in 1/128th of your total blocks before you reach full allocation.

On 06/28/2013 10:36 AM, Wayne Smith wrote:
> Having equal space taken by production files and snapshots doesn't mean
> every block has changed (assuming you have more than one snapshot). Each
> snapshot is kept intact. So if your database changes any 1/4 of itself for
> each snapshot and you have 4 snapshots, you have equal production and
> snapshot space usage (assuming no dedup/compression).
> Cheers, Wayne
>
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>

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Received on Fri Jun 28 2013 - 18:05:11 CEST