topic Re: Write I/O Block Size in ONTAP Discussions

Write I/O Block Size

General — Wed, 04 Jun 2025 12:14:03 GMT

Hello,

Does anyone know how to get Write I/O block size for a volume/LUN by way of System Manager, Unified Manager or CLI for a NAS filer?

I would assumne it should be pretty easy within Unified Manager but I'm not finding the data.

Thanks in advance!

Re: Write I/O Block Size

Ontapforrum — Fri, 20 Sep 2019 21:15:35 GMT

It's much easier via CLI for cDOT.

If you run this command:
SANCL1::> qos statistics volume characteristics show

You get output for all the volumes in the cluster, just look for Request size that's your IO size.

If you want to know the IO size for specific volume then use the following command:

SANCL1::> qos statistics volume characteristics show -volume v_dmz -vserver san01
Workload ID IOPS Throughput Request Size (IO Size) Read Concurrency
--------------- ------ -------- ---------------- ------------ ---- -----------
v_dmz 21451 6 3.00KB/s 512B 66% 0

Re: Write I/O Block Size

General — Fri, 20 Sep 2019 21:49:48 GMT

Is that only READs? What about writes? Nothing with a timeline?

Re: Write I/O Block Size

General — Fri, 20 Sep 2019 22:02:27 GMT

Nevermind, I miss read. Thanks for the help!

Re: Write I/O Block Size

paul_stejskal — Tue, 24 Sep 2019 14:41:38 GMT

statistics volume show has a field for op size. There is also one for statistics lun show. However you can always take the bytes/second divided by # of IOPs.

For example, 21,626,880‬ read byte/second divided by 330 read IOPs would be 65535.

Note: stats volume is limited to 64k because the WAFL file layer does 64k. At the protocol level it gets split up into multiple 64k chunks. You can use stats nfsv3/smb2 or stats lun to get a readout of op size > 64k.

Documentation: https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-cmpr-950%2FTOC__statistics.html&lang=en

Examples for node shell/7-mode: https://kb.netapp.com/app/answers/answer_view/a_id/1035917/loc/en_US

Note: Documentation is more generic to stats/statistics commands, but should give you an idea.

Let me know if you need more help getting the syntax.