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How to tell actual bus speed

Bill Gillespie
Occasional Contributor

How to tell actual bus speed

Is there a way to tell the actual bus speed being used on a Proliant server (ML 370 or ML 570). We are running Linux. I am suspecting that the Smart Array 5302 cards we have are not actually performing at Ultra 3 speeds (160 MB/sec per channel). On 2 different servers with different disks in different RAID configurations we continue to see a top read speed of about 70 MB/sec.

We have Ultra 3 disks on one and Ultra 320 disks on the other.

I was wondering if perhaps the bus speed was the problem. Could there be some setting causing this?

On the ML 570 we have 2 5302 cards and they are in separate busses than the tape and network cards. I think there are 3 actual busses with 2 slots each on this server.

Any suggestions would be appreciated!
4 REPLIES
Martin Breidenbach
Honored Contributor

Re: How to tell actual bus speed

160MB/s and 320MB/s are the maximum bus transfer speeds. A single hard drive is much slower. You need 5-10 drives and do sequential read operations to actually get to that value.

Note that this is the data transfer rate over SCSI bus. If the drives are doing random reads and have to move their heads the results are MUCH slower.
Bill Gillespie
Occasional Contributor

Re: How to tell actual bus speed

Yes, we do have 7 disks in a single RAID 5 set on one of the dual busses on the shelf and connected to one of the channels on the 5302. That RAID 5 set is set up as a single mount point, and we consistently get a read rate of 70 MB/sec. If we reconfigure to RAID 0, again with multiple disks, we still only see 70 MB/sec. This is the same max speed on both machines.

I understand that the Ultra 160/320 are the maximum bus speeds. I also understand that Ultra 2 has a maximum bus speed of 80 MB/sec, which somewhat lines up with what we are actually seeing. So I was wondering if something might be causing the 5302 card to be running in an Ultra 2 compatible mode and choking our throughput.
Martin Breidenbach
Honored Contributor

Re: How to tell actual bus speed

My manuals here say that a sequential read data rate of 8-16 MB/s per drive can be expected. Now that's a wide range...

I can check tomorrow whether insight manager can display scsi bus speed (no proliant here at home).
Bill Gillespie
Occasional Contributor

Re: How to tell actual bus speed

We are able to get from 50 MB/sec from a single disk (U320 or U160, 10k) in a RAID 0 config. We begin to top out quickly though with multiple disks.