Hello,
I have what looks like a firmware or design performance bug with some
74G WD Velociraptors WD740ADFD-00NLR5 (firmware 21.07QR5). Sequential
read speed (as measured with 'hdparm -t') drops-off with NCQ depths
greater than 2.
Queue-depth(cmds) Speed(MB/s)
1 84
2 84
3 46
5 39
10 39
20 44
31 36
The speed given is the best of 10 - the system was under light load (I
couldn't completely unload it, unfortunately).
Western Digital helpfully suggested that I contact my Linux vendor...
The system is a Tyan server with a Core2Quad Q6600 @ 2.40GHz, and an
ICH9 running Debian 5.0 - kernel 2.6.26-2-openvz-amd64, SATA ports in
non-RAID/AHCI/native mode.
I measured the speed like this:
for i in {1..31} ; do echo $i > /sys/block/sda/device/queue_depth ; echo
-n "$( cat /sys/block/sda/device/queue_depth | head -c -1 )," ; for j in
{1..10} ; do (hdparm -t /dev/sda | egrep -o
'[[:digit:]]+\.[[:digit:]]+[[:space:]]+MB/sec' | head -c -1 ) ; done ;
echo ; done | sed 's/ MB\/sec/,/g'
... and created a chart and max speed data in openoffice:
http://buttersideup.com/files/wd-raptor-NCQ-bug-1.pdf
with a second run here:
http://buttersideup.com/files/wd-raptor-NCQ-bug-2.pdf
Any comments or suggestions welcome - I'd be happy to repeat the test
using a different benchmark if anyone can suggest a command-line they'd
like run?
Cheers,
Tim.
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