Mailing List Archive

Snapshot reserve
We tend to have very large file systems (largest NetApp one is > 40tb),
and the default 20% snapshot reserve starts to be a huge waste of space.
Is there any good reason not to just set it to 0%? The snapshotted files
aren't limited by the reserve, so what's the real point of it? A lot of
times we end up with reserves that are only a few % in use, so it's
truly wasted space. I've been setting those ones to have small reserves,
and the discussion ensued whether it's worth having any reserve at all.

Thanks.

Vince
Blue Sky Studios
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Re: Snapshot reserve [ In reply to ]
> We tend to have very large file systems (largest NetApp one is > 40tb),
> and the default 20% snapshot reserve starts to be a huge waste of space.
> Is there any good reason not to just set it to 0%? The snapshotted files
> aren't limited by the reserve, so what's the real point of it? A lot of
> times we end up with reserves that are only a few % in use, so it's
> truly wasted space. I've been setting those ones to have small reserves,
> and the discussion ensued whether it's worth having any reserve at all.
>

Hi Vincent,

Setting snap reserve to 0% is fine. The only down side is that
when you delete files that are in snapshots, you don't see any
space freed up. You get the space back later when all snaphots
containing the deleted files are deleted.



Steve Losen scl@virginia.edu phone: 434-924-0640

University of Virginia ITC Unix Support


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AW: Snapshot reserve [ In reply to ]
Hello there,

the reason for the reserve is that it is not counted towards your free space on the filesystem, so let's say you create a volume with 100GB and the default snap reserve of 20%, only 80GB will be available in the volume, so you can fill it up until it reaches 80GB of data.
If you do not use snapshots at all, you can disable snap reserve, snap schedule and set the nosnap and nosnapdir options to on for this volume. When I need to do that, I usually use the following commands:

snap sched VOLUME 0 0 0
snap reserve VOLUME 0
vol options VOLUME nosnap on
vol options VOLUME nosnapdir on

There are several options you can apply to a volume that tell the filer what to do if the snap space is growing rapidly or is exceeding the configured amount of snap reserve, f.ex. volume autogrow, deletion of old snapshots, etc.
If you do not have snap reserve configured, DFM and other monitoring tools will also not be able to tell you if there's something wrong with the current amount of snapshots and the free space in the volume will go up and down whenever a snapshot is created or deleted, so basically, it's just a logical thing to separate snapshot data from real data and should help you in keeping an eye on your storage, it is not necessary at all to have a snap reserve defined for NFS or CIFS volumes, but it cerrtainly makes sense.

Bye,
Alex

-----Urspr√ľngliche Nachricht-----
Von: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] Im Auftrag von Vincent Liggio
Gesendet: Donnerstag, 10. November 2011 23:34
An: toasters@teaparty.net
Betreff: Snapshot reserve

We tend to have very large file systems (largest NetApp one is > 40tb), and the default 20% snapshot reserve starts to be a huge waste of space.
Is there any good reason not to just set it to 0%? The snapshotted files aren't limited by the reserve, so what's the real point of it? A lot of times we end up with reserves that are only a few % in use, so it's truly wasted space. I've been setting those ones to have small reserves, and the discussion ensued whether it's worth having any reserve at all.

Thanks.

Vince
Blue Sky Studios
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Re: Snapshot reserve [ In reply to ]
The snapshot reserve is really there for filesystem which are exposed to end users, who may not be aware of the behaviour of enterprise storage.

Normally, if you use snapshots, then if a user deletes a file, it does not actually free any space on the storage system (assuming the file is in a snapshot). The end user may find that confusing ("I just deleted that big file but my space used didn't go down"). So by hiding some of the volume space from the user in the snapshot reservation, you make the user think that when the delete a file that space really is freed up.

NetApp best practise for volumes which aren't traditional NAS mounts/shares (e.g. volumes which contain LUNs) is to set the snapshot reservation to zero. You might also want to do that for volumes which end users don't directly see, such as backup destinations. And of course if you don't take snapshots then you don't need a snapshot reservation.

Setting a snapshot reservation will also prevent an end user from causing snapshot failures in the volume by filling it up, but only provided the snapshot reservation is not full.

Jeremy

--
Jeremy Webber
Senior Systems Engineer
Animal Logic Pty Ltd
T: +61 2 9383 4837
F: +61 2 9383 4801


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