Nimble snapshot space usage

[marcusburrows]

When a Nimble snapshot starts to consume space, where is the space deducted from? Is it deducted from the Volume or from the underlying Pool?  Also, does the snapshot space count against Folder usage?

Thank you.

[JohnAthaide · Accepted solution]

@marcusburrows : Hello Marcus,

Nimble Snapshots are ROW ( Redirect on Write) which means the Snapshot would lock the original volume and any modification/deletion of the data protected by the Snapshot would be redirected to a newer block in the Storage Pool. 

[marcusburrows]

Thank you. Sorry to ask another question, just to be clear.  So does the active file system + snapshotted blocks = volume usage capacity? Or is it active file system = volume usage capacity and the snapshotted blocks are deducted from unused Storage Pool space?  I hope that makes sense?  Thank you again.

[Sheldon Smith]

Hi Marcus,

Not sure what you mean by 'active file system'. A volume is created with a virtual size, say, 2 TiB. The 2 TiB is what the host OS sees for the volume size. As the host writes data, it's gathered within the Nimble's memory, deduped and compressed according to the volume's settings, and the result along with other volumes' data is written to the Pool. There are layers of pointers between the volume's logical block and what's written to the physical disks. As data changes and new data comes in, the process repeats and pointers are updated as required.

When a snapshot happens, the volume's pointers would be duplicated for the snapshot. From that point on, as data changes and new data comes in, it's gathered within the Nimble's memory, deduped and compressed according to the volume's settings, and the result along with other volumes' data is written to the Pool. And pointers are updated as required. (Whoa! Deja vu!) 

Only what's written by the host OS to the volume is seen by the host. Regardless of the number of snapshots, the host can write the full 2 TiB to the volume. However, considering any deduplication and compression, that does not mean 2 TiB will need to be allocated to hold the volume's 2 TiB.

If you do a command line "vol --list" you will see the volume's (virtual) size, 2 TIB, and how much is currently used.
If you do a "vol --info name --verbose" you will also see the snapshot usage, which is not part of the volume usage.

[marcusburrows]

Although I wasn't clear in my question, you have told me what I needed to know! Many thanks!

This is the bit I meant:

Only what's written by the host OS to the volume is seen by the host. Regardless of the number of snapshots, the host can write the full 2 TiB to the volume.

you will also see the snapshot usage, which is not part of the volume usage.