Average Disk perfomance with Backup Battery Write cache (BBWC) installed

[Al_56]

To improve disk performance on our database and VMWare servers, l installed the BBWC (346914-B21 128MB unit) on the 6i RAID controller.

The host OS on all systems is RHEL 4.3 Linux (actually CentOS) and when the systems booted l saw the RAID cache upped to 192 Meg, and a message stating that write performance would improve once the battery had charged.

On 2 of the servers we are running 146gig 15k drives in RAID 1 and using "hdparm -t /dev/cciss/c0t0" l can see only a moderate increase in disk performance (from 87MB per second to 105MB per second).

On other servers (where the OS was installed with the BBWC in place) l have seen huge write performance differences of between 135-140MB per sec on some servers with a RAID 5 config, and up to 195MB per sec on another.

l ran these tests when the servers were quiet to eliminate external disk i/o influences as much as possible.

Is hparm a good test mechanism? If not what else can l try to gauge disk performance on linux?

l do not wish to install the Array management software as it taints the kernel, and this can crash VMWare or severely slow its performance for some reason.

How can l check and set the BBWC settings manually without installing the HP array software? Is there anything l can do?

Thanks in advance,

Alan

[Steven E. Protter]

Shalom Alan,

I would suggest that you run the same set of read/write scripts.

If you have an oracle or mysql database, your write test should be to that database, because this is rough on the disks and the most realistic test.

The best overall tools for measuring performance on Linux are the sar tools.

The test must be the same on all systems to make the results meaningful.

SEP

[Al_56]

Thanks SEP,

Is there a way of determining if the cache card is fully enabled an configured correctly without installing the array tools?

l would be happy to know that the system is correctly configured to automatically take advantage of the cache card upon its installation.

Thanks,

Alan

[TwoProc]

I've not looked in quite a while, but I believe that if you have ILO (Integrated Lights Out - free from HP on an HP computer) installed on that computer, you can see that the BBWC is turned on from there.

[Al_56]

l do have ILO on the server.

What command do l use to find out? What should l look for?

Thanks in advance.

Alan

[TwoProc]

I'll look into it this AM.

[TwoProc]

Alan,

I'm sorry, I thought that I'd seen it in ILO, but I checked, and I can't. It might there in one of the other optional licensed packages (and maybe I saw it there in trial version). Please excuse the bad information.

[Al_56]

Thanks very much much for checking mate.

Greatly appreciate it.