[lug] Debugging I/O performance

Rob Nagler nagler at bivio.biz
Tue Mar 13 10:13:16 MDT 2018


We have some Dell m620s in a m1000e chassis. I was switching around disk
controllers to figure out if the Dell H310 (non-RAID) worked better than
the S110 (non-RAID or AHCI) was faster. One of the m620s has twice as slow
disk I/O, and I can't figure out why.

There are no errors in the logs. lshw, hdparm, etc. are identical. I walked
through the BIOS config. Also, identical. Simple CPU benchmarks are
identical. Fresh installs with the same CentOS 7 kickstart config (minimal
install).

Many details have been documented here:
https://github.com/radiasoft/devops/wiki/DellRAID#performance

The two identical machines are f2 and f3 with H310s. f4 is almost the same
but uses an onboard controller (AHCI).

I can afford to swap around m620s with some in our diskless cluster, which
would avoid the problem. However, it seems to me there's something wrong,
and I should understand what it is.

Any ideas how to determine what's causing the performance difference?

Thanks,
Rob
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