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n00b
- Joined
- Jun 12, 2013
- Messages
- 31
One of my hard disks is being excruciatingly slow, and I can't quite figure out why. Hope you can help.
How slow is it?
For comparison, another hard disk provides:
Both of these are Samsung Spinpoint F4 EG 2TB disks. They are connected to Dell H200 controllers, using VT-d pass-through to the machine that was running the above.
I've tried connecting the dodgy disk (sdm) to to a different H200 HBA, and to use a different SAS-SATA breakout cable. This disk is consistently producing poor performance.
When I do a large streaming read, eg. dd if=/dev/sdm of=/dev/null bs=1024768, iostat says that 50% of my cpu is stuck in iowait state. But how do I tell what's the cause?
Any idea what might be wrong / what to look for?
How slow is it?
Code:
# hdparm -Tt /dev/sdm
/dev/sdm:
Timing cached reads: 15042 MB in 2.00 seconds = 7526.71 MB/sec
Timing buffered disk reads: 26 MB in 3.26 seconds = 7.99 MB/secFor comparison, another hard disk provides:
Code:
# hdparm -Tt /dev/sdl
/dev/sdl:
Timing cached reads: 20710 MB in 2.00 seconds = 10365.46 MB/sec
Timing buffered disk reads: 428 MB in 3.01 seconds = 142.31 MB/secBoth of these are Samsung Spinpoint F4 EG 2TB disks. They are connected to Dell H200 controllers, using VT-d pass-through to the machine that was running the above.
I've tried connecting the dodgy disk (sdm) to to a different H200 HBA, and to use a different SAS-SATA breakout cable. This disk is consistently producing poor performance.
When I do a large streaming read, eg. dd if=/dev/sdm of=/dev/null bs=1024768, iostat says that 50% of my cpu is stuck in iowait state. But how do I tell what's the cause?
Code:
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sdm 48.50 6208.00 0.00 12416 0
avg-cpu: %user %nice %system %iowait %steal %idle
0.25 0.00 0.25 49.25 0.00 50.25Any idea what might be wrong / what to look for?
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