FreeBSD 5.3b7and poor ata performance

[Scott Long]

Xin LI wrote:
> Hi, Mike
> 
> On Tue, Oct 19, 2004 at 04:18:12PM -0400, Mike Jakubik wrote:
> 
>>Xin LI said:
>>
>>
>>>Unfortunatelly I can reproduce similiar problem when using Ultra320 under
>>>mpt(4) and a version of Adaptec's SCSI card (maybe aic, or something else,
>>>which I have to go to my office to find out).  Additionally the problem is
>>>not FreeBSD specific, with a Linux installation, it shows poor performance
>>>too.  (No RAID configuration, though).
>>>
>>>I found that block size does influence performance greatly.  With a block
>>>size of 131072 I got peak read performance at about 70MB/s, but that's
>>>all.
>>>I did not have the necessary knowledge at the time I have did the test
>>>last
>>>month, so I got only the result and thought that I have made something
>>>wrong and hoped someone to correct me with no luck :-(
>>
>>Hrm, i tried your block size, and the performance is even worse:
>>
>># dd if=/dev/da0 of=/dev/null bs=131072 count=2000
>>2000+0 records in
>>2000+0 records out
>>262144000 bytes transferred in 8.688651 secs (30170852 bytes/sec)
> 
> 
> You may want to try other block sizes, like 65536, 262144, 524288, 1048576
> or so.  The peak performance block size depends heavily on hardware...
> 
> Cheers,

This won't really matter.  physio will chop the blocks up into 128k 
segments, and GEOM will cut them again into 64k segments.  Other than
a minor amount of coelscing in these stages, it won't make a difference.

Scott