14.55 TiB Volume limit?

[Hung Phan]

Hi all. I’m new to the forum and new to FreeNAS. I have a questions about FreeNAS diskspace overhead.
I’m trying to build a new storage server with FreeNAS-9.2.1.5-RELEASE-x64 (80c1d35) to replace our existing Windows 2008 Storage server Essential. I’m building it with an HP DL180 G6 with an LSI SAS9211-8i adapter flashed with 19.00-IT firmware.
I have 8 x 4TB SATA drives that I want to create a volume as a VM datastore for a couple of VMware ESXi 5 hosts. The ESXi hosts and the FreeNAS server will be connected via 10G network.
FreeNAS is running off an 8GB USB flashcard. We’re planning to use RaidZ2.

When I try to create a volume with the 8 drives with RaidZ2, I got available Capacity: 14.55 TiB
That doesn’t seem right. 8 x 4 = 32 TB Total minus two parity 2x4 = 8. Avaiable space should be 24 TB minus some overhead FreeNAS reserved for swap and such. However instead of something a little less than 24TB what seems to be available was 14.55 TB.
How could this be? That’s a LOT of overhead if that was the case.

When I limit the volume to use 6 disks, the setting changes to RaidZ and the capacity remain at 14.55 TiB.
Is 14.55 TB some sort of limit for FreeNAS? I don’t see that mentioned anywhere.

Does anyone have any insights on this?

Thank you.

 

[gpsguy]

In the attached picture, you selected the equivalent of a striped mirror. That's why you are only seeing ~14.6Tib.

Try grabbing the circular gizmo and putting all the drives on a single row (top row), with all 8 drives selected to give you a RAIDz2 volume.

The striped mirrors will probably give you better performance that RAIDz2. I'd do some benchmarking with both scenarios before committing to one or the other.

 

[Hung Phan]

Oh thank you so much gpsguy! I didn't realized that you could use the gui that way. I drag them all to the top row and the capacity is now 21.82 TiB. A lot closer to what I was expecting. Thank you!