Is it file-system consistent when I take volume snapshot on CIFS or NFS volume?

[NetappNewbie-Roy]

Hi Tech Guys,

Is it file-system consistent when I take volume snapshot on CIFS or NFS volume? Thanks for reply.

[AlexDawson]

The NetApp side is fine - but client systems may have files opened or unflushed writes. In general though, you would have bad luck if this were an issue - most of the time it's fine.

[NetappNewbie-Roy]

Thanks Alex for the info. I would like to know if I cannot stop the CIFS or NFS connection, and someone is transferring a large file to the NAS and I take a snapshot on the volume in Netapp. Will the I/O be stored in some buffer else where and the file not be included in the snapshot as it is still duting I/O? Or  the file willl be included in the snapshot but it cannot be opened as it is not a complete file?  Or the FAS will wait until all file I/O complete before it takes snapshot?

[AlexDawson]

Think of it this way: If you have a 1GB file that is just full of "AAAAAAAAA" .. and you're overwriting it with "BBBBBBBB", and you take a snapshot halfway through, the file available in the snapshot will be half "BBBBB", then half "AAAAAAA". It won't be either the original or the planned version, but it will be there. The next snapshot will be all "BBBBBBB", and the previous will be all "AAAAAAA".

If you're using the system for CIFS for general purpose file storage, this isn't usually a problem - most files are small enough that writes happen almost instantly.

If you're using CIFS (SMBv3) for Microsoft HyperV, or MS SQL Server, or NFS for VMWare, this can be a bit more of a problem, as the write may have been something important for the virtual machine's filesystem. We have Snapmanager tools to enable VMs to pause, flush, then we take a snapshot. Is this what you're planning on using them for? or just interested in how it works?

[NetappNewbie-Roy]

I am planning if I should use NFS or FC for my Hyper-V server farm. I will need file-system consistent snapshot and SQL application-consistent snapshot. In case FC is better, I will need brocade FC switch besides the storage as I don't have brocade right now.

So by your explanation, I should use FC instaed of NFS because snaphot a NFS volume cannot maintain file integrity and FC LUN snapshot can get help from SnapDrive and SnapManager to get application consistent snapshot?

[AlexDawson]

So for HyperV, you would be using SMBv3, not NFS (while I'm more familiar with VMware, there's plenty of articles writing about NFS/HyperV it not working, so I feel confident saying that).

We have got SnapManager for HyperV ( https://library.netapp.com/ecm/ecm_download_file/ECMLP2631434 ), and it supports SMBv3, FC or iSCSI. It sounds like you'd rather not do FC, so that leaves iSCSI and SMBv3. So no, you don't need to buy an FC switch if you don't want to.

[NetappNewbie-Roy]

Thanks Alex. One final question, If I use CIFS share as shared storage and I put vhdx file on it. The content of the vhdx keeps changing as application like web server is putting photo and videos in it.  Please correct me if I am wrong. snapmanager for hyperv is similar to VSC in vSphere, and if I want to have file system-consistent snapshot on the volume with vhdx files. I need some application level snapmanager as well. Can I make a volume snapshot by snapmanager for hyperv then it will contact SQL snapmanager to make sure the vhdx is application consistent? thanks for advice.

[AlexDawson · Accepted solution]

Yes, Snapmanager for SQL supports talking to Snapmanager for Hyper-V to make consistent snapshots. This is detailed in this document - https://library.netapp.com/ecm/ecm_download_file/ECMP1649830

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