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QES RAID capacity missing

Posted: Mon May 13, 2019 11:02 pm
by dkleeman
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?

Re: QES RAID capacity missing

Posted: Tue May 14, 2019 12:30 am
by storageman
It is what it is. Other calculator here.
https://wintelguy.com/zfs-calc.pl

Re: QES RAID capacity missing

Posted: Tue May 14, 2019 1:57 am
by dkleeman
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

Re: QES RAID capacity missing

Posted: Tue May 14, 2019 4:19 pm
by storageman
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

Re: QES RAID capacity missing

Posted: Tue May 14, 2019 6:43 pm
by dkleeman
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).

Re: QES RAID capacity missing

Posted: Tue May 14, 2019 6:58 pm
by storageman
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.

Re: QES RAID capacity missing

Posted: Mon Sep 09, 2019 6:07 pm
by joechao