zpool iostat operations question

[TxAggieEngineer]

System is an X10 with 3x 8TB mirrored vdev's, 16GB ZLOG SSD and 400GB SSD read cache.

When I run "zpool iostat tank 2" I see read bandwidth but the vast majority of the time the read operations column is zero. There are four VM's currently running off of this X10 using iSCSI so it's lightly loaded right now but I would think I would see *some* read operations when there's something greater than zero in the read bandwidth column. Any thoughts as to why there are no read operations showing up most of the time?

root@HQ-SAN-2b[~]# zpool iostat tank 2
capacity operations bandwidth
pool alloc free read write read write
---------- ----- ----- ----- ----- ----- -----
tank 476G 21.3T 2 59 58.7K 3.33M
tank 476G 21.3T 0 150 0 9.49M
tank 476G 21.3T 0 0 1.88K 0
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 152 0 7.85M
tank 476G 21.3T 0 0 7.97K 0
tank 476G 21.3T 0 120 0 6.01M
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 127 5.96K 4.70M
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 111 0 3.69M
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 110 7.52K 5.20M
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 134 0 6.16M
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 216 0 14.1M
tank 476G 21.3T 0 0 0 0
tank 476G 21.3T 0 115 0 3.66M
tank 476G 21.3T 0 0 0 0

 

[Arwen]

Please include all your hardware, including amount of memory.

Their is a GUI page for Memory & ARC usage, as well as a command line arc summary script. Both will tell if your ARC & L2ARC / Cache are being used to the fullest. That is their intent after all, reduce disk reads. (Free memory is wasted memory, so ZFS uses as much as it can.)

 

[TxAggieEngineer]

Please include all your hardware, including amount of memory.

Their is a GUI page for Memory & ARC usage, as well as a command line arc summary script. Both will tell if your ARC & L2ARC / Cache are being used to the fullest. That is their intent after all, reduce disk reads. (Free memory is wasted memory, so ZFS uses as much as it can.)

All the specs of the X10 are published so I didn't think there was a need to re-list them here. The system has 32GB RAM (https://www.truenas.com/x-series/).

If I'm understanding your response, you are saying that the fact there are zero IOPS indicates the data in the "read bandwidth" column is being read from ARC or L2ARC?

 

[Arwen]

Sorry, I "guessed" you were using one of the Supermicro X10 series system boards, which have different features.

I don't know for sure, but yes, I am "guessing" again that your reads are being serviced from ARC or L2ARC.

Perhaps someone with more knowledge on the subject can answer. Or give you a better idea of how to test that hypothesis.