2120S poor performance

[Michael E.Conlen]

On Dec 9, 2004, at 12:49 PM, Jin Guojun [VFFS] wrote:

> I do not remember where the original problem of 2120s was posted.
> The read in RAID 5 mode is 40-56 MB/s, where write rate is 5-13 MB/s.
> The most problem is at writing to RAID, average around 8 MB/s.
> SCSI buses self is Okay because doing multiple R/W without RAID
> can get maximum disk I/O. Soft RAID, like Vinum, also slows down
> disk array performance. SO, it sounds like that RAID design has
> big overhead to kill the performance.
>
> dd if=/dev/aacd0s1b of=/dev/null bs=128k count=20000
> dev/null bs=128k count=20000
> 20000+0 records in
> 20000+0 records out
> 2621440000 bytes transferred in 61.651078 secs (42520587 bytes/sec)
>
> Adaptec guy told me that this is a design issue. One older model,
> which may be out of market, is performing better, but I would not
> expect a large difference as soft RAID do not give better performance.

Poorly implemented RAID-5 will often times incur a read operation for 
every write so that it can calculate the checksum value. Some 
implementations will identify when an entire stripe is being written 
and avoid it when possible.

Try tuning the FS so that the blocks in the FS match up with the stripe 
size in the controller. I believe this will force every write to be a 
stripe.

--
Michael Conlen
meconlen at obfuscated.net