Re: RAID-5 streaming read performance

On Thu, 2005-07-14 at 11:16 +1000, Neil Brown wrote:

On Wednesday July 13, mingz@ele.uri.edu wrote:

quoted

On Thu, 2005-07-14 at 08:38 +1000, Neil Brown wrote:

quoted

On Wednesday July 13, jdc@uwo.ca wrote:

quoted

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