Disk IO issues

Ricky Zhou ricky at fedoraproject.org
Wed Dec 31 22:26:27 UTC 2008


On 2008-12-31 10:49:56 PM, Xavier Lamien wrote:
> Could you perform an hdparm -tT on that disk ?
/dev/sde:
 Timing cached reads:   2668 MB in  2.00 seconds = 1336.06 MB/sec
 Timing buffered disk reads:  1024 MB in  3.01 seconds = 340.69 MB/sec

> Also, output an strace against your cat & dd commands.
> 
> if my memory is good enough, cat use mmap() which is faster than
> read() (which is used by dd)
I just straced dd and cat, and it looks like cat is using a block size
of 4096 bytes while dd is using 512 bytes.  I *think* they were both
just using read().  Perhaps dd if=/dev/sde of=/dev/null bs=4096 would be
a better command to compare against.

Thanks,
Ricky

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