RE: [Xen-users] Very slow drives, I/O - DMA issues?

["Ulrich Windl" <ulrich.windl@xxxxxxxxxxxxxxxxxxxx>]

On 21 Feb 2007 at 21:33, Steffen Heil wrote:

[...]
> >hdparm -tT /dev/hd?
> 
> /dev/hda:
>  Timing cached reads:   266 MB in  2.00 seconds = 132.84 MB/sec
>  Timing buffered disk reads:  144 MB in  3.01 seconds =  47.82 MB/sec
[...]

Just for curiosity: As I'd expect XEN to buffer "virtual physical reads", did 
anybody repeat the commend twice in succession? That is
hdparm -t /dev/hda
hdparm -t /dev/hda

I have made two tests here: First SLES9 without XEN (hardware RAID1, SCSI):
/dev/sda:
 Timing buffered disk reads:  182 MB in  3.03 seconds =  60.13 MB/sec
/dev/sda:
 Timing buffered disk reads:  162 MB in  3.01 seconds =  53.76 MB/sec

Then SLES10 x86_64 with XEN 3.0.2 (hardware RAID1, SAS):
/dev/sda1:
 Timing buffered disk reads:  202 MB in  3.01 seconds =  67.17 MB/sec
/dev/sda1:
 Timing buffered disk reads:  170 MB in  3.03 seconds =  56.17 MB/sec

While the performance doesn't look verby bad, I think I can get about 150MB/s 
from 
the SAS RAID without XEN. The CPUs involved were a Pentium-4 with 2.4GHz, and 
an 
Opteron at 2.6GHz.

Regards,
Ulrich


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