Optimal configuration of TrueNAS to be used for backup

[NASitall]

I am a newbie with TrueNAS and hitting a roadblock with write performance.
Hoping someone can give some pointers to improve write performance.
I have TrueNAS scale installed on PowerEdge R730XD server
Dual Intel Xeon E5-2680v4 processors (HT disabled) with total 28 cores.
256GB SK Hynix 32GB DDR4 2400MHz ECC RAM
PowerEdge server is connected to 2 x Seagate EXOS X 5U84 block storage connected via single HBA 9500-16e adapter.
Each Storage unit consists of 84 x Seagate 20TB SAS 4k 12Gbps HDDs (ST2000NM002D)
Created a single pool on each storage - With 6 x RAIDZ3 VDEVs Each VDEV consists of 14 x 20TB drives.
Have set a log ssd(735GB) device and also metadata device (735GB SSD) for this pool.
The purpose of this TrueNAS is to use it for backing up PB data from Isilon.Data consists of several small files adding upto PB storage.
Ethernet 10GBASE-T
Pool configuration – Sync disabled, Compression level off, atime off, Record size =128k
zpool get all |grep ashift nas_pool1 ashift 12 local
Any suggestions is much appreciated.

 

[jgreco]

Hoping someone can give some pointers to improve write performance.

With 6 x RAIDZ3 VDEVs Each VDEV consists of 14 x 20TB drives.

Well there's your problem. Don't use RAIDZ3, it;s significantly slower than RAIDZ2. Don't use VDEV's that are 14 wide. Way too wide, don't go more than maybe 10. And finally, DON'T USE RAIDZ AT ALL. It imposes significant performance penalties. Use mirrors.

connected via single HBA 9500-16e adapter.

Might also be a problem; I don't have one handy but I would be a bit concerned about what driver this appears under.

Have set a log ssd(735GB) device and also metadata device (735GB SSD) for this pool.

You cannot just use any random SSD for SLOG. What are you using? You should also mirror the metadata because loss of a metadata device is loss of the pool.

Make sure you have not enabled dedup either.

Ethernet 10GBASE-T

Also a poor choice. But when giving specs, identify WHAT kind of thing this is ("Intel X540" etc) so that we can tell you something more specific.