smart array 532 poor performance

[ivan_77]

I have ml370 server with 2 2.4GHz CPU. There are 2 controllers in the server - smart start 5312 connected to the disk enclosure (real performnance - 20-40MB/s - which is good) and another controller smart start 532 which is connected to the internal disk cage of the server - 4HDD RAID5 and 2HDD RAID1 but the write performance of this controller is very poor - 1-4MB/s. The firmware/drivers are upgraded and the system is w2k with sp3. Is this dramatic shortage of performance caused of the fact that 532 does not have the write cache?

[Derek Parmenter]

Baltay,

You may well be correct with the lack of write cache slowing down your server. However I would also check your IRQ levels on your server, just in case the 532 is clashing with another device.

The operating system will not get a confirmation of write until the RAID controller has finished writing to disk because you have no write cache. If you had the write cache, then the operating system gets a confirmation of write when it is in the cache memory (if you read up on write back cache, it will explain this principle).

In RAID5 for every write, it will need to cacluate the parity. This will be an overhead on the RAID engine that may well be slowing down performance. You may find that perfomance on your RAID1 is better than the RAID5 on 532, this would be expected, if cache is an issue, but still not as good performance as your 5312.
Derek

[ivan_77]

thank u, i think one irq is beeing shared on the pci bus on the ml370 server. Do u have any further recommendations?

[Derek Parmenter]

IRQ sharing in itself is not an issue, however I have experienced servers that have shared the wrong interupts e.g.

IRQ3 - Com2
IRQ4 - Com1
IRQ6 - Floppy
IRQ7 - LPT
IRQ8 - System
IRQ12 - Mouse

These are defaults and if the devices are enabled, they will more than likely use these. The RAID controller should not share with any of these devices.
Is your 532 sharing with any other device and if so what is it ?

[ivan_77]

no all the pci cards are on the same interrupt 15

[Derek Parmenter]

As long as they are all PCI, it will not cause clashes by sharing interrupts. There are debates as to sharing and not sharing in that you may well get better performance by not sharing.

You could try changing the interrupt, but it does sound as though the write cache is potentially your solution for performance. It will be cheaper (downtime dependant) to change the IRQ, so that could be a worthwhile first step.