QNAP NAS Community Forum

I have two identical TES-1885U NAS devices, each with 12 x 12 TB disks. NAS1 uses QTS operating system and NAS2 uses QES. QES has ZFS and a number of benefits (per QNAP).

Using RAID-6 with a hot spare, NAS1 has a storage pool size of 98.14 TB and NAS2 has a storage pool size of 86.11 TB. This is an additional loss of one whole drive for no reason that I can see. I do not believe that I have made an error in accidentally assigning too few disks. The achieved size is consistent with the calculation on this QNAP page: https://enterprise-nas.qnap.com/en/calculator/.

I cannot see any reference to QNAP or anyone else writing that QES with ZFS reduces the available disk space. Does anyone have any comment on this?

It is what it is. Other calculator here.
https://wintelguy.com/zfs-calc.pl

Are we saying that ZFS RAIDZ2 is known to consume 14% more space than RAID6? I cannot find a general reference to this.

For example, from http://www.zfsbuild.com/2010/05/26/zfs-raid-levels/:

RAIDZ2 (RAID6)
RAIDZ2 is like RAID6. You get double parity to tolerate multiple disk failures. The performance is very similar to RAIDZ. How To Create RAIDZ2 Zpool

Some stuff here. Enjoy!
https://wintelguy.com/2017/zfs-storage-overhead.html

BTW if you want better data integrity use QES
If you want the best performance use QTS

I am grateful for your replies and I have carefully reviewed them both and the links you have helpfully provided. I think that you are implying that ZFS RAID-Z2 is worse than RAID-6 and that this is (a) generally known and (b) that my QNAP-derived figures are in line with standard ZFS. I was not aware of the former point but I now see this. I think that QNAP could usefully make it more clear on this page: https://www.qnap.com/en/how-to/faq/arti ... -enhanced/.

On your second implied point, I think that QNAP are using more space than the calculator shows. Using 12,000 GB disk size and a 4 KiB sector size and RAID-Z2 the overhead is calculated to be 88.57 TiB. The practical losses for QTS/RAID6 seems to be simply the 2 disk overhead (18.2%). Thus QES/RAID-Z2 is 8% worse according to the calculator. This is, as you say, "what it is" according to wintelguy. However, the QNAP achieved usable space is 86.11 which is noticeably worse (2.0% as a percentage of the raw capacity).

I agree, with QES, QNAP are really pushing their enterprise capabilities.
I would email them on the space but I'd be surprised if they come back with a meaningful answer.

Refer to this FAQ:
https://www.qnap.com/en/how-to/faq/arti ... ecord-size

last time for 2.1.0 fw update
qes drop limits of max drives per raid group

https://docs.qnap.com/esnas/2.1.0/en/GU ... 978E1.html

fyi