Re: RAID-5 streaming read performance

[Ming Zhang <mingz@ele.uri.edu>]

On Thu, 2005-07-14 at 11:16 +1000, Neil Brown wrote:
> On Wednesday July 13, mingz@ele.uri.edu wrote:
> > On Thu, 2005-07-14 at 08:38 +1000, Neil Brown wrote:
> > > On Wednesday July 13, jdc@uwo.ca wrote:
> > > > Here's a question for people running software raid-5:  do you get
> > > > significantly better read speed from a raid-5 device than from it's
> > > > component partitions/hard drives, using the simple dd test I did?
> > > 
> > > SCSI-160 bus, using just 4 of the 15000rpm drives:
> > > 
> > > each drive by itself delivers about 67M/s
> > > Three drives in parallel deliver 40M/s each, total of 120M/s
> > > 4 give 30M/s each or a total of 120M/s
> > > 
> > > raid5 over 4 drives delivers 132M/s
> > why here a 132MB/s instead of 120MB/s (3 * 40MB/s) as u mentioned? any
> > factor lead to this increase?
> > 
> > 
> 
> I did another test over 10 times the amount of data, and for 34M/s for
> 4 concurrent individual drives, which multiplies out to 136M/s.  The
> same amount of data of the raid5 gives 137M/s, so I think it was just
> experimental error.
ic. thanks for explanation. yes, agree. 

it seems that u can get a near linear performance with decent SCSI HW
while what we can get from SATA is not good. :P

Ming

> 
> NeilBrown