Unexpected ZVol space usage

[DavieC]

I have some zvols using much more space than expected, and can't figure out why.

We have presented a couple of zvols to our ESX servers. The zvols provisioned at 62TB.
On each of these we have a single 55TB disk presented to a windows guest. These disks are about 75% full.

These virtual disks were vmotion'ed from another SAN platform where space usage was as expected (but it was a traditional block type SAN)

TrueNAS is reporting these zvols are using122TB and 123TB respectively.
There are no snapshots.
Block size was left at default 64KiB

We cant figure out why there is a 100% overhead in space usage.
We have other installations doing the same thing without the large space overhead (there is some overhead, but only small amount)

Running on TrueNAS-SCALE-23.10.1.3

Any pointers on where to look would be much appreciated, we are pulling our hair out here.

dave

 

[DavieC]

Humm, I just found this thread, I wonder if this is my problem:

The allocated space for my Zvol is significantly surpassed by its current usage.

Hello, I'm running TrueNAS Scale as my SAN, with individual Zvols assigned to each SAN drive. One specific Zvol hosts my Plex VM, initially configured for 8TiB, yet it's consuming over 14TiB. I maintain backups in two locations, both on-site and off-site, making it quite costly. I'm puzzled...

www.truenas.com

 

[chuck32]

I wonder if this is my problem:

Did you provision them as sparse or thick? You mention you're not using snapshots though.

 

[DavieC]

Did you provision them as sparse or thick? You mention you're not using snapshots though.

Thick provisioned

We did have snapshots configured for replication, but have deleted these while trying to find the source of our problem. We do want to be able to replicate these zvols to another system.

This comment makes me thing it's this refreservation setting, but havent tested.

"When you don't set a zvol to be sparse at creation, a refreservation size is set, meaning it will want the same size as the zvol to be reserved when taking a snapshot (to allow the entire zvol to change without filling the disk)"


Thanks

 

[chuck32]

Thick provisioned

Sorry for the late reply, you could use sparse zvols instead or follow the thread you linked (although I have no experience in that, so I can't vouch for anything that comes with it).

You'd need to check the documentation yourself but without specifying anything else

zfs send path/to/your/zvol | zfs receive -v path/to/your/zvol_new will provision the new zvol as sparse ;)

This will create a snapshot and transfer the current state of the zvol to the new zvol.