Snap Vault files location question

[KKChan]

HI,

We have a FAS2650 for production, the volumes has been setup to take snapshot for hourly, daily & weekly schedule. It will store the snapshots for a short period in case any fast recover need. The snapshot files will also use SnapVault to another FAS2554 for long term keeping. So I need to check and make sure in FAS2650 have enough space for snapshot files. And I just notice that on FAS2554, the vaulted snapshot files were also located in the Snapshot reserve area of the volume on FAS2554. Is this correct? Why not use the normal capacity of the destination volume? If this is true then I will have limit capacity for the vaulted Snapshot files since they are located in the reserve area. Can I use the whole volume capacity for the snapshot files?

Also when I try to enable storage efficiency on FAS2554 volume, I notice that it has warning say "Storage efficiency cannot be enabled for offline volumes and mirror destination volumes". Is it means that I can't enable this on my FAS2554 volume (this volumes were snapmirror destination volume under Snap Vault)?

[sgrant]

Hi, the SnapVault snapshots will be held in the snapshot reserve of the volume like all other snapshots. There is also no problem in using the sapce in the volume to hold snapshots, however as a best practice you would normally size the snapshot reserve (percent-snapshot-space) to hold all snapshots and then monitor the capacity of both the volume and snapshot reserve. Or you can drop the snapshot reserve of the destination volume to 0% (assuming relationship is SnapVault and not SnapMirror) and just monitor the capacity of the volume.

That being said, it looks like the SnapMirror relationship to the FAS2554 is not of type XDP (i.e. SnapVault), since you cannot enable storage efficiencies on the SnapMirror type DP destination volumes as they are read only (until the relationship is broken). However, you will be able to enable them on SnapVault destination volumes. Please check the relationship type using the snapmirror show -fields type command, should show "XDP" in the "Type" column.

Hope this helps.

Thanks,

Grant.

[KKChan]

HI Sagrant,

Thanks for your reply.

Current on the source box (FAS2650), I'm keep monitoring the data capacity and snapshot reserve to make sure enough space is available. I have problem last week when the snapshot reserve space not enough and casue the volume offline. I exoand the volume capacity and increase the snapshot reserve % to ensure enough space there and keep my eye on the snapshot size trend.

On the deestination box (FAS2554) it is use for only store for the old snapshots which transfer from 2650. When I create the relationship between two box, I choose relationship type is "Vault", from your command it also report the type is XDP.  So is it means that I can enable the storage efficiency option? I can click the option to enable but I just saw the warning message so want to clarify it before I enable the option. So if it is "XDP", it can be enable the storage efficiency?

At beginning when I create the volume on destination box (FAS2554), I set the snapshot reserve to 0% as though the Vault snapshot will locate in the volume. But when I check it now I notice that it have red word showing "snapshot overflow". After I increase the snapshot reserve %, the red words gone. So I suppose the Vault snapshot files on the destination box still locate in the snapshot reserve area. Am I right? The volume in this box has nothing to connect and just use for the old snapshot backup files storing. So what should I cofnigure on this volume to make it all use for the Vault snapshot files?

[sgrant]

So, definately being SnapVault volume, I therefore think the warning you might be seeing could be related to enabling compression, from the Data Protection Using SnapMirror and SnapVault Technology Guide...

If the secondary volume has additional compression enabled, storage efficiency is not preserved

Storage efficiency on all data transfers in SnapVault relationships is not preserved when the secondary volume has additional compression enabled. Because of the loss of storage efficiency, a warning message is displayed when you enable compression on a SnapVault secondary volume. After you enable compression on the secondary volume, data transfers are no longer storage efficient. You can reenable storage efficiency on data transfers after you disable compression on the secondary volume.

Therefore you'd just want to match the primary storage efficiencies to maintain the savings ensuring all data is transferred efficienctly; you should not see any error messages/warning. For SnapVault destination volumes you can and should (unless there are specific reasons) enable the storage efficiencies.

You can also safely ignore the messages about the snapshot overflow since this is by design, once acknowledged the red will go away. It is easier to manage with a 0% snap reserve, since you only need to alert against the volume capacity.

Let me know if you have any other query.

Thanks,

Grant.

[KKChan]

Hi Grant,

Thanks for your advice.

I try to enable the storage efficiency and notice that under the details section the compression status is "Disable". I think this is like what you mention no compression on the destination volume. On last run details I can saw there is both deduplication and compresssion saving figure. I think that is the similare figure show in the source volume. 

Further on the snapshot reserve setting area. My source volume is a LUN, so do I need to create a LUN in destination volume? Since the destination volume is use for store the snapshot files, just thinking there should be no reason for me to create and have the same size LUN in the destination volume (as source box). Will this configuration (the volume without LUN create and only let it use for snapshot files) be a better one?

[sgrant]

OK, so looks like the stroage efficiencies is sorted?

SnapVault is a copy of the source data (including any LUN) that is periodically updated to keep the data in the secondary volume up to date with changes made in the primary data. Therefore the destination volume for the SnapVault, while it is writable i.e. you can change the snapshot reserve different to the source volume, it does contain a read only copy of the source LUN. You cannot change this LUN, which reflects the state of the source LUN as at the time of the last update (just as SnapMirror would). This is needed as the base against which all the changed blocks held in the SnapVault snapshots are referenced.

You just need to worry about ensuring there is sufficent space in the volume for the number of SnapVault snapshots you wish to hold.

Please see the Data Protection Using SnapMirror® and SnapVault® Technology for reference: https://library.netapp.com/ecm/ecm_download_file/ECMLP2494079

Does this explain it for you?

Thanks,

Grant.