[ProgClub programming] Hard drive performance

John Elliot V | ProgClub jj5 at progclub.org
Tue Jun 11 01:25:32 AEST 2019

All of a sudden I'm getting really poor performance from a bunch of my
hard disks. I'm not sure what the pre-problem performance was like,
except that it wasn't a problem, and now, suddenly, it is.

The disks in question are in a ZFS RAID5 array. They're a broad mix of
old left over drives which I have salvaged to build this server, there
are some details here:


ZFS 'zpool status' reports an ongoing 'scrub' operation:

  scan: scrub in progress since Sun Jun  9 00:24:02 2019
  431G scanned out of 4.38T at 463K/s, (scan is slow, no estimated time)
  0B repaired, 9.61% done

as you can see it's reading at a measly 463K/s, which is dribble, it
should be more like 46.3M/s... I ran 'iotop' on the same server and it's
only operating at around 500K/s read too.

I checked the temperature and that seems to be within acceptable range:

 root at trust:~# hddtemp /dev/sd[abcd]
 /dev/sda: WDC WDS120G1G0A-00SS50: 42°C
 /dev/sdb: ST3000VN000-1H4167: 40°C
 /dev/sdc: ST33000650NS: 45°C
 /dev/sdd: WDC WD30EFRX-68EUZN0: 38°C

I would note that sd[bcd] are magnetic drives, and they all have
differing rotation speeds, in case that might be an exacerbating factor.

Can anyone suggest what I can do to diagnose and hopefully fix whatever
it is that's leading to this poor drive performance..? I don't believe
I've encountered a problem like this before...

May the Force be with you,
John Elliot V
|_|O|_| ProgClub
|_|_|O| Because every programmer needs a good club!
|O|O|O| https://www.progclub.org/
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