CBRC digest files backup

[raphael@schitz.net]

When backup a VM with CBRC enabled, both vm_name-digest.vmdk and vm_name-digest-flat.vmdk files are not backed up.
Is it an expected behaviour?
VSP 5.5 and VBR 7.0.0.871 here.

[foggy]

We actually haven't considered backing up these files before, you're the first to rise this question. As far as I can get, CBRC is a sort of dynamic cache for VM disk blocks, which is stored in host's memory and periodically re-calculated, so there's not much sense in backing up this data.

Btw, have you tried to restore VMs that have this feature enabled?

[raphael@schitz.net]

Hi foggy,

Actually, the digest file is used by the CBRC cache mecanism so if you restore the "data" vmdk without the digest vmdk, you need to recreate it. Even if the digest is a bit dirty, it could still bring cache hit so it would be nice to back it up. BTW, the digest file path is present in the "data" vmdk file but the VM is able to boot without it, you just have no cache.

I working on a big VDI infrascture to push this feature and size the VM are dedicated per user and backed up with veeam, this could be a NO GO for the customer because each time a VM would be restore, the digest file recreation would be needed.

Thanks for your help

[foggy]

Seems to make sense in cases where it could allow to avoid digests re-calculation. We will discuss the reasonability of backing up this information. Thanks for the heads up.

[raphael@schitz.net]

Thanks foggy. If you need a customer request to speed this up, just let me know

[dellock6]

Just a quick note: VMware has started a new project called VAIO (vSphere APIs for I/O Filtering) that will be the new solution for caching plugins, and seems they will drop at the same time their own CRBC technology, so I'm not so sure we should look into CRBC and instead focus more on the new upcoming technology.

[raphael@schitz.net]

Thanks Luca but i heard about CBRC during a vmworld VSAN session so maybe this feature will evolve to save some SSD writes.

[raphael@schitz.net]

As expected, CBRC (aka View Storage Accelerator) is still recomended by VMware http://www.vmware.com/files/pdf/techpap ... torage.pdf