snapshot occuyping huge space with no much data change

[selvi]

snapshot occuyping huge space. But there is no such actual data change. Snap delta is showing 10 am snapshot as huge in size but snap reclaimable between the same 2 snapshots very less size. Volume has only qtrees and are all quota set. no luns are present inside it and dedup not enabled. Snapmirror is enabled and it also tranfers huge data to its destination.  I have copied below the snap delta output.

From Snapshot To KB changed Time Rate (KB/hour)

--------------- -------------------- ----------- ------------ ---------------

hourly.0 Active File System 1520728 0d 01:26 1057693.353

hourly.1 hourly.0 8292032 0d 02:59 2764266.617

nightly.0 hourly.1 19814772 0d 09:59 1981807.501

hourly.2 nightly.0 302148 0d 08:00 37761.944

hourly.3 hourly.2 561224 0d 02:59 187091.989

hourly.4 hourly.3 6841328 0d 03:00 2280231.534

Pls note the difference between the nightly.0 & hourly.1 is 19814772( 19 GB) where the snap reclaimable space between the same two snapshot is only  297 MB.

What could be the proble.

Any suggestions on this pls

regards,

selvi

[aborzenkov]

It is not necessary a problem and cannot be answered without much more detailed information. But some points

- Snapshot “grows” also when you delete data.

- Snap reclaimable shows how much space would be freed if named snapshot were deleted. Effectively it shows you how much unique data is contained in snapshot

Now in your example consider following scenario

First you make snapshot hourly.2

Then you make snapshot nitghly.0 without changing anything

Then you delete 20G of data and make snapshot hourly.1

If you look at shapshot “size”, hourly.2 would be zero (nothing has changed) and nightly.0 would be 20G. But if you now run “snap reclaimable nightly.0 hourly.1” it will show you zero bytes, because all data is shared between hourly.2 and nightly.0. Deleting nightly.0 would just shift space accounting to previous snapshot.

[selvi]

Yes, I understand that, even if there are deletions,  snapshot still occupy the space of deleted data. This particular volume has only qtrees and with quota set. I have taken quota report to find the used size at various times within a day and on different days, i find no major reduce or increase in size.  the changes in qtree used size shown in quota report is only in KBs or ver few MBs.

qtrees are having only user files and folders. no application is accessing it.

Is there a way to find which qtree is undergoing deletions and additions

regards,

selvi

[aborzenkov]

Are they CIFS shares? It is known that many Microsoft applications will create completely new file instead of making changes in-place; that is the reason for file folding option on NetApp. Many users editing many files could well account for this amount of changes.

[selvi]

yes it is CIFS shares. But no applications are accessing. it contains only user files mainly of word, ppt etc. Please tell me more in detail abt the below line

"Microsoft Applications completely create new file instead of making changes, that is the reason for file folding option"

I have gone throught the file folding option in the guides, however, i am not very clear on how it works.  Currently file folding is OFF. can I trun it on now just like that without any maintanence. If I do so, will i be able to recover some space. its a snapmirror source. So, does it have any effect on the snapmirror relationship.

[aborzenkov]

I am afraid I cannot give any reference, this was from discussions during NetApp training. Office applications create new file version and then move it over original one.

CIFS file folding compares file content with previous version in snapshot and discards data that was not changed (replacing it with reference to snapshot). So if you change single character in 4M files without file folding you get 4M in snapshot and 4M in active file system. With folding you hopefully get just 4K extra in snapshot.

CIFS file folding can be enabled at any time. It won’t have any effect on existing snapshots, nor on any file that already was changed, only on newly changed files. If may help with SnapMirror by reducing size of snapshots and thus transfer size.

Do not forget that it adds additional load (filer now has to physically compare full file content); it means extra CPU, disk load, cache pollution etc. Be prepared to monitor filer to catch performance degradation.

[selvi]

which means without file folding, if 2 KB of data in 50 MB  file chages, which is being held by snapshot; this change will increase the snapshot space by 50MB in size. Is my understanding correct.

[aborzenkov]

That is correct, assuming that old version is removed and new version put in place.