On Wed, 31 Dec 2008, Ricky Zhou wrote:
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.
Ok, that explains the difference between dd and cat. Now why is the rest of it so bad.
-Mike