Possibly Incorrect Volume Usage Reported/ ReFS on ZFS

[andyb85]

Hello,

I'm using FreeNAS to present an iSCSI lun to veeam for backups. I've carved a 70 TB LUN out of our 160 TB pool.
Our Backup jobs utilize the ReFS block cloning feature.
Windows reports 13.5 TB are free of this 70 TB LUN, but in FreeNAS, It's showing 140 TB used of 160TB.
The 140 TB would be the size should the ReFS block cloned backups be rehydrated. When this usage hits 100% in FreeNAS the iSCSI lun will go in to read only mode on the windows side effectively making the LUN useless.

Any ideas why this is happening?

I'm running FreeNAS-9.10.2-U5 (561f0d7a1)

 

[Ericloewe]

Windows reports 13.5 TB are free of this 70 TB LUN, but in FreeNAS, It's showing 140 TB used of 160TB.

Snapshots? Absolutely atrociously inefficient space usage caused by RAIDZ?

 

[andyb85]

Hello,

There are no snapshots. Its' almost like zfs is counting the blocks mapped by refs block cloning as being used instead of being just mapped metadata. Hope that makes sense

 

[Ericloewe]

Are you using RAIDZ?

 

[andyb85]

It's raidz2

 

[Ericloewe]

Well, there's your problem. RAIDZ can be atrociously inefficient when dealing with the small blocks characteristic of block storage. That and performance concerns pretty much dictate that mirrors are needed for most block storage applications.