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Re: Need Help Understanding Snapshots

jason92s
Aspirant

ReadyNAS 312 Need Help Understanding Snapshots

We're about to pull the trigger on a ReadyNAS 312 with either two 2TB or 4TB drives. We have about 290GB of data files. Ideally we'd like to have daily snapshots, but I'm unsure how much data a snapshot takes. If I go daily, does that mean each snapshot will have 290GB of data in it, and I'd get about 5 snapshots before pruning started? Thank you.

Message 1 of 34
RX
Luminary
Luminary

Re: Need Help Understanding Snapshots

Just want to share these articles below if in case have not yet came across with it since might provide you with usable info:

http://kb.netgear.com/app/answers/detai ... erating-my

http://kb.netgear.com/app/answers/detail/a_id/24478

http://www.netgear.com/images/ReadyNAS% ... -76104.pdf
Message 2 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

Hi, yeah I did find those article, and they are helpful. I'm still just not grasping the concept of how much data a snapshot uses. Thank you.
Message 3 of 34
RX
Luminary
Luminary

Re: Need Help Understanding Snapshots

Sharing these forum thread links below since its related to your concern. Hope that you will be enlightened:

https://www.readynas.com/forum/viewtopi ... 50&t=74657

viewtopic.php?f=7&t=76917
Message 4 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

I initiated a chat support session and the person said Snapshots work like the Time Machine does in Mac. I haven't found any other information to support this, but if that's the case, then basically the first snapshot is a full "backup" and each subsequent snapshot is a differential "backup". I'm really hoping that's the case.
Message 5 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

It's wrong to think of the snapshot as a backup. I think the support agent gave you misleading information at best.

The answer to your question depends on the file churn after the snapshot is created.

Let's use 100 10MB files in a share as an example, and assume no file fragmentation at the start.

When you first make a snapshot it actually takes no space. All the datablocks in the snapshot are shared by the main share and the snapshot.
So there is 1000MB total: 1000MB in common; 0 MB only in the snapshot; 0 MB only in the share.

Now imagine that fifty 10 MB files are deleted on the main share. The original datablocks remain in the snapshot, but are no longer shared.
So there is 1000MB total: 500MB in common; 500 MB only in the snapshot; 0 MB only in the share.

Furthermore, imagine that one file is completely changed in the main share. Again, the original datablocks end up in in the snapshot alone, and we have 10MB of more total space.
So there is 1010MB total: 490MB in common; 510 MB only in the snapshot; 10MB only in the share.

Now lets modify the first 5 MB of another file. That 5 MB can no longer be in common, total space goes up 5 MB. The version of the file in the main share is fragmented, the version in the snapshot is not fragmented.
So there is 1015MB total: 485MB in common; 515 MB only in the snapshot; 15MB only in the share.

Now lets add 10 new files of 10 MB each to the share. These aren't in the snapshot, but only in the share.
So there is 1115MB total: 485MB in common; 515 MB only in the snapshot; 115MB only in the share.
Message 6 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

I can't tell you how helpful that is StephenB. Makes perfect sense and I think Netgear should append this to their KB articles.
Message 7 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

Glad it helps. Of course tracking all this becomes more difficult as you create more snapshots.

But the principles are the same:
Whenever a shared datablock is deleted in the main folder, it becomes snapshot space.
Whenever a shared datablock is modified in the main folder, CoW creates a new copy of that datablock in the main folder, and the original ends up in one or more snapshots.

It's not a backup, because if there were data corruption in a shared block, then the snapshot and the main folder are both corrupted.
Message 8 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

Very helpful. Main reason we like this is we use Previous Versions in Server 2008, and I can't tell you how many times people want to go back 3 hours for a Word document they messed up. If we did hourly snapshots this would be a lifesaver. I guess my only issue is you have to "clone" the entire snapshot to get a single file restored, but from my reading you just clone the snapshot to a new location and grab the file you need. Hopefully I'm understanding that correctly 🙂
Message 9 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

Previous versions works with these snapshots too. 🙂
Message 10 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

Oh, I mean we will no longer be in a server environment once we go to ReadyNAS. Just too few people to justify the added expense and overhead. Where are these previous versions being stored?
Message 11 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

jason92s wrote:
Oh, I mean we will no longer be in a server environment once we go to ReadyNAS. Just too few people to justify the added expense and overhead.
Ok.

But your users will still be able to right-click on a file in windows explorer and select "Previous Versions" just like they do now.
Message 12 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

Wait...Really? I thought that was server based the whole time! So, if I have a share on my NAS called Data that is mapped as the J drive, a user can right click it still and see previous versions?
Message 13 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

jason92s wrote:
...a user can right click it still and see previous versions?
Yes as long as snapshots are on for the share.
Message 14 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

That's very cool! So the NAS just takes on the added space for storing the previous versions huh?
Message 15 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

jason92s wrote:
That's very cool! So the NAS just takes on the added space for storing the previous versions huh?
Yes. In your case, you'd see all versions captured in your hourly snapshots. (Not sure, but I think you won't see duplicates, just distinct versions).

If a file was changed twice between snapshots, you'd miss a version.

BTW the automatic snapshots are pruned back. Hourly snapshots are kept for 48 hours, daily snapshots are kept for 4 weeks, weekly snapshots are kept for 8 weeks, and monthly snapshots are kept indefinitely. That will also thin the available versions over time.
Message 16 of 34
jason92s
Aspirant

Re: Need Help Understanding Snapshots

This is very cool!!! Thanks again for your help. Very much appreciated.
Message 17 of 34
mdgm-ntgr
NETGEAR Employee Retired

Re: Need Help Understanding Snapshots

If the usage on the volume exceeds 95% the oldest automatic snapshots will be removed to get the volume usage back below 95%.
Message 18 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

mdgm wrote:
If the usage on the volume exceeds 95% the oldest automatic snapshots will be removed to get the volume usage back below 95%.
Yes, I forgot to mention that.

It's much better not to let the NAS get that full of course.
Message 19 of 34
BaJohn
Virtuoso

Re: Need Help Understanding Snapshots

StephenB wrote:
In your case, you'd see all versions captured in your hourly snapshots. (Not sure, but I think you won't see duplicates, just distinct versions).
ALL snapshots are visible, NOT just distinct versions.
StephenB wrote:
Hourly snapshots are kept for 48 hours, daily snapshots are kept for 4 weeks, weekly snapshots are kept for 8 weeks, and monthly snapshots are kept indefinitely. That will also thin the available versions over time.
I believe that the automatic monthly snapshots MAY be deleted, when the discs get full, default 95% alterable via the shell.
However the manual snapshots are NEVER deleted, except by you of course.

EDIT:- Sorry guys ... started reply before lunch and continued after, resulting in duplication (the second point).
The first point still stands and is new to the post .......All snapshots are visible.
Message 20 of 34
mdgm-ntgr
NETGEAR Employee Retired

Re: Need Help Understanding Snapshots

The threshold is alterable using the shell not via the UI.
Message 21 of 34
BaJohn
Virtuoso

Re: Need Help Understanding Snapshots

mdgm wrote:
The threshold is alterable using the shell not via the UI.
Corrected as it was misleading.. I was using the English settings in general, not specifically the 'Settings' options in the GUI.
Message 22 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

BaJohn wrote:
StephenB wrote:
In your case, you'd see all versions captured in your hourly snapshots. (Not sure, but I think you won't see duplicates, just distinct versions).
ALL snapshots are visible, NOT just distinct versions.
All snapshots are certainly visible. But I was talking specifically about what shows up on the "previous versions" right click, not about snapshots per se.

I have double-checked this, and only distinct versions show up in "Previous versions". I have a share with 35 snapshots taken over the past three months. Files that haven't changed over that period come up with "no previous version found". Files that have changed don't give me 35 versions to choose from, only the ones that are actually different. All these files are in all 35 snapshots.
Message 23 of 34
BaJohn
Virtuoso

Re: Need Help Understanding Snapshots

StephenB wrote:
All snapshots are certainly visible. But I was talking specifically about what shows up on the "previous versions" right click, not about snapshots per se.

I have double-checked this, and only distinct versions show up in "Previous versions". I have a share with 35 snapshots taken over the past three months. Files that haven't changed over that period come up with "no previous version found". Files that have changed don't give me 35 versions to choose from, only the ones that are actually different. All these files are in all 35 snapshots.
Thanks for clearing up the ambiguity.
jason92s wrote:
I can't tell you how helpful that is StephenB. Makes perfect sense and I think Netgear should append this to their KB articles.
I wholeheartedly agree, and as I have mentioned elsewhere, hope none of the useful information in some of the posts is not lost in the transfer to a new forum.
Message 24 of 34
StephenB
Guru

Re: Need Help Understanding Snapshots

I think "previous versions" is a very nice feature ReadyNAS feature, and perhaps under-publicized.

If you know what file you want to roll back, it is much faster/more convenient than browsing through a ton of snapshots.
Message 25 of 34
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