[lug] Debugging I/O performance

[Simos]

On Tue, 13 Mar 2018 10:13:16 -0600
Rob Nagler <nagler at bivio.biz> wrote:

> 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

You said you already ran hdparm so this may be pointless but are the
smartctl output & perf tests similar as well?

Simos