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What's the difference between rp7420 and rp4440 in performace?

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Lee, Jones
Occasional Advisor

What's the difference between rp7420 and rp4440 in performace?

Hi, Guys,
I just add one rp4440 with my old rp7420 to form a cluster. Both of them have the same speed CPU (PA8900 1.1GHz) and amount of memory (12GB). The only difference is the rp4440 having 4G SAN HBA, but rp7420 only 2G. I find that older rp7420 always double the GBL_DISK_PHYS_IO_RATE compare with the rp4440. Does this is a normal situation? And does the rp4440 have better performace compare with the rp7420 if we don't consider the SAN card? Thanks for your kindly help in advance.
BR
Jones Lee
6 REPLIES
Matti_Kurkela
Honored Contributor

Re: What's the difference between rp7420 and rp4440 in performace?

You should examine the I/O architecture of your servers. See the HP QuickSpecs entries:

rp7420:
http://h18006.www1.hp.com/products/quickspecs/11895_div/11895_div.HTML

rp4440:
http://h18006.www1.hp.com/products/quickspecs/12034_div/12034_div.HTML

A rp7420 has 14 dual-channel slots that can provide 1060 MB/s bandwidth to a PCI-X card. The other 2 slots have only a single channel, and can offer only 530 MB/s bandwidth.

In a rp4440, only 2 PCI-X slots have the dual-channel feature. That means most of the slots can offer only 530 MB/s bandwidth.

If the 4G HBAs are not installed into those high-performance slots on the rp4440, you get only half the I/O bandwidth you might expect. That would line up with your GBL_DISK_PHYS_IO_RATE results.

The rp7420 and rp4440 are roughly at the same technology level (especially with identical CPUs), but the rp7420 has a more I/O capacity. It needs to have that, because it has more room for expansion.

With identical RAM and CPUs, I would have expected rp7420 and rp4440 to be roughly equal in performance. Maybe the rp7420 would have some performance advantage because of its better I/O performance, depending on the required I/O configuration (number of NICs/HBAs/etc.). But a two-to-one difference in favor of the rp7420 is a bit much: to me, it suggests the rp4440 might be misconfigured.

MK
MK
Lee, Jones
Occasional Advisor

Re: What's the difference between rp7420 and rp4440 in performace?

Dear MK,
Appreciate your helpful information. I did not notice the different speed between I/O slots. Could you help to explain more details of the IO_RATE? Does it mean the I/O system calls issued in the certain interval? The slower the IO bandwidth the lower IO rate? or in an opposite direction?
Thanks for your kindly help.
BR
Jones Lee
Matti_Kurkela
Honored Contributor
Solution

Re: What's the difference between rp7420 and rp4440 in performace?

The MeasureWare documentation explanice GBL_DISK_PHYS_IO_RATE like this:
--------
The number of physical IOs per second during the interval.
Only local disks are counted in this measurement. NFS devices (and DUX
devices on HPUX 9.0) are excluded. This includes all types of physical
IOs to disk, including virtual memory IO and raw IO.
This is calculated as

GBL_DISK_PHYS_IO_RATE =
GBL_DISK_FS_IO_RATE +
GBL_DISK_VM_IO_RATE +
GBL_DISK_SYSTEM_IO_RATE +
GBL_DISK_RAW_IO_RATE
-------

As far as I understand, this does not calculate system calls, but the actual SCSI/FC requests the kernel makes to the disks. Assuming that both servers make same kinds of requests on average (and I don't see why they wouldn't in this case), there should be a fairly direct relationship between the I/O rate (number of requests) and the actual amount of data transferred.

The slot bandwidth is a hardware limitation: it is the maximum data rate the slot can provide in ideal circumstances.

If the slot bandwidth is insufficient for the HBA, it limits the amount of data that can be transferred in a given time, and thus limits the rate of the disk I/O operations.

MK
MK
Lee, Jones
Occasional Advisor

Re: What's the difference between rp7420 and rp4440 in performace?

Dear MK,
Thanks for your kindly help which helps me to understand more about it. I'll check which slots HP CE installed the HBAs. I'll update the result later.
BR
Jones Lee
Lee, Jones
Occasional Advisor

Re: What's the difference between rp7420 and rp4440 in performace?

Dear MK,
Bingo, I use "rad -q" and "ioscan" to verify. HP CE did install the FC cards on the 66 MHz IO slots. Thanks for your great help.
BR
Jones Lee
Lee, Jones
Occasional Advisor

Re: What's the difference between rp7420 and rp4440 in performace?

rp4440 has fewer 133 MHz PCI-X slots then the rp7420. And HP CE install the FC cards on the slower (66 MHz) PCI-X slots, so the IO bandwidth of rp4440 only half of the rp7420, therefore because the GBL_DISK_PHYS_IO_RATE has only half of the rp7420 too.
Thanks for MK's help.