Hi Adam,
Zitat von Adam Goryachev <adam@xxxxxxxxxxxxxxxxxxxxxx>:
Hi,
I have a RAID5 array which consists of 8 x Intel 480GB SSD, single
partition on each covering 100% of the drive.
[...]
I'm finding that the underlying disk utilisation is "uneven" ie, one
or two disks is used a lot more heavily than the others. This is
best seen with iostat:
iostat -x -N /dev/sd? 5
This will show 5 second averages... so we should expect the average
utilisation of all disks to be equal ( I expect, I am probably wrong).
Ignoring the first output, since that is values since the system was
booted, I've copied three sample from after that.
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s
avgrq-sz avgqu-sz await r_await w_await svctm %util
sdf 128.00 194.00 86.80 141.20 897.70 1289.60
19.19 0.04 0.18 0.16 0.20 0.13 2.96
sdh 110.80 138.60 83.40 139.20 808.80 1063.20
16.82 0.08 0.34 0.21 0.42 0.31 6.96
sde 120.80 162.00 90.60 117.80 866.40 1073.60
18.62 0.09 0.42 0.12 0.65 0.38 7.84
sdb 141.80 184.60 110.60 130.60 1104.30 1219.20
19.27 0.04 0.15 0.14 0.16 0.11 2.64
sda 126.00 153.80 89.80 120.40 921.00 1048.00
18.73 0.13 0.61 0.14 0.96 0.57 12.08
sdg 132.20 168.40 113.00 122.80 1037.60 1116.80
18.27 0.05 0.21 0.28 0.15 0.15 3.60
sdd 122.20 180.80 99.80 135.60 958.40 1219.20
18.50 0.04 0.16 0.20 0.13 0.10 2.40
sdc 112.80 178.60 87.40 115.20 824.00 1128.80
19.28 0.17 0.85 0.43 1.17 0.75 15.20
[...]
As you can see, sdc (and sda) has a much higher utilisation compared
to all the other drives, but we can see the actual reads/writes are
similar across all drives.
looking at those numbers, it might not be the (effective) utilization
that's higher, but the time the SSDs spend handling the requests.
As you already ruled out model issues for sda, further probable causes
that I'd check might be
- a different firmware level for sda
- disk problems (anything useful in the SMART numbers?)
- connection issues (are all disks connected to the same (type of)
controller?)
I can't comment on the RAID parameter questions, though.
Regards,
Jens
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