avgrq-sz maxes out at 1024 for lvm devices

[John Anthony <chirayithaj@gmail.com>]

All:

Doing a test to identify the best stipe / block sizes for high end SAN storage.

The test involves setting up LVM raw devices of stripe sizes 128K and beyond - and using dd with block sizes of 128K and beyond.

Issue is :-

Beyond block sizes of 512 K (1024 sectos) - the avgrq-sz does not increase as reported by iostat -x. As if there is a limit. Is this an LVM imposed limit - dm imposed - or even more generic ?

leading upto 1024 sectors avgrq-sz - increases with block size as expected.

Where is the limit ? Is it configurable ?

-JAC

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