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Luminary

Snapshot question(s)

A while back I elected to enable snapshots for most shares on one of our ReadyNAS systems.

 

Time went on, I ignored the snapshot topic until today I noticed that snapshots apparently take up a reasonable amount of disk space.

 

A good share of our storage is occupied by essentially static data – seldom changed.  My notion was that the snapshot was like an incremental backup – if nothing changed then the ‘snapshot’ would be very small in size.  That does not seem to be the case.  Shares that have not changed have lots of snapshot space allocated/used.

 

On top of that I elected daily snapshots thinking that the amount of space used would be small and the ReadyNAS would have nothing better to do while taking the snapshots.

 

The question is what is in a snapshot – is it a clone of the share each time it is executed or just the recent changes or ??

Model: RND4220|ReadyNAS NV+ 4TB (2 X 2TB)
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Guru

Re: Snapshot question(s)

What NAS model is this, and what firmware it is running?

 

Assuming you are running OS 6,  you should start with this explanation from some years ago: https://community.netgear.com/t5/Using-your-ReadyNAS-in-Business/ReadyNAS-312-Need-Help-Understandin...

 

Files that aren't being re-written or deleted won't create more snapshot space usage.  So you should sort out what is going on.

 

Also, I don't recommend using the default "smart" snapshot setting - the reason is that there is no way to limit retention (and monthly snapshots are retained for ever).  Instead use the custom snapshot setting, and set a reasonable retention limit for each share.   If the space usage seems excessive, then adjust the retention accordingly.

 

Personally I use 3 months for most of my shares.  One is shorter (2 weeks), and one has snapshots off.

 

 

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Guru

Re: Snapshot question(s)

What NAS model is this, and what firmware it is running?

 

Assuming you are running OS 6,  you should start with this explanation from some years ago: https://community.netgear.com/t5/Using-your-ReadyNAS-in-Business/ReadyNAS-312-Need-Help-Understandin...

 

Files that aren't being re-written or deleted won't create more snapshot space usage.  So you should sort out what is going on.

 

Also, I don't recommend using the default "smart" snapshot setting - the reason is that there is no way to limit retention (and monthly snapshots are retained for ever).  Instead use the custom snapshot setting, and set a reasonable retention limit for each share.   If the space usage seems excessive, then adjust the retention accordingly.

 

Personally I use 3 months for most of my shares.  One is shorter (2 weeks), and one has snapshots off.

 

 

View solution in original post

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Luminary

Re: Snapshot question(s)

Thanks -- the reference to prior art was helpful.

The suggestion on using 'custom'  was also helpful.

 

 Netgear shopuld incorporate this into some article/KB info.

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Guru

Re: Snapshot question(s)


@Digital999 wrote:

Thanks -- the reference to prior art was helpful.

I'm glad it helped.  One aspect I didn't cover back then was the impact of defragmentation.

 

If a file is modified in place (for instance,when a live database is updated), the main copy ends up fragmented, and the original ends up in the snapshot.  The total storage is the original + the modified data blocks.

 

If you then defrag the file in the main share, you end up disconnecting the two versions - so the total storage becomes the original + the full modified version.

 

Note that in many situations this doesn't matter.  For instance, word and excel documents are completely re-written when you save them, so the storage ends up as the original +full modified version anyway.

 


@Digital999 wrote:

 

The suggestion on using 'custom'  was also helpful.

Netgear should incorporate this into some article/KB info.


I really don't understand what Netgear was thinking when they defaulted to indefinite retention.  They really should change that (adding a setting for it).  Without it, you need to go in periodically and manually delete the older ones - otherwise the volume runs out of space, which really isn't something you want to let happen.

 

I've suggested that a description of how snapshots work (and how they impact space) should be in a kb article in the past, but nothing ever came of it.

 

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