topic Re: P400 with BBWC AND physical disk write cache in Disk Enclosures

P400 with BBWC AND physical disk write cache

Daniel Gilanyi — Sat, 14 Jun 2008 07:44:03 GMT

Dear all,
after installing the battery kit on a P400 controller, could I get some extra performance if I also enable the Physical Disk Write Cache option in the controller utility? (It is disabled by default and I know it's not battery backed up but the power supply is redundant, so maybe it worth the risk if only the performance counts...)
thx!

Re: P400 with BBWC AND physical disk write cache

TTr — Sat, 14 Jun 2008 12:37:58 GMT

At one point you say "after installing the battery kit" and at another "I know it's not battery backed up". Which is it?

If you don't have the BBWC you already know the risk. At the same time the array might not enable the write cache if it senses that the BBWC is not installed.

Re: P400 with BBWC AND physical disk write cache

Daniel Gilanyi — Mon, 16 Jun 2008 04:26:39 GMT

As I know the battery kit is for the controller (card)'s cache memory (256m in my case) but there is also a smaller local cache in the disks, which can be enabled/disabled from the config utility.
It seems these are disabled by default.

Re: P400 with BBWC AND physical disk write cache

Patrick Terlisten — Mon, 16 Jun 2008 06:07:02 GMT

Hello Daniel,

there are two parts: You can add cache memory to the controller, and you can add a BBWC (a batterey module for the cache) to the controller.

What kind of extension did you add? Only cache or cache and BBWC?

Yes, you can get a little more performance if you enable the physical drive cache, but I wouldn't do it. This cache isn't battery backuped, so you can lose data, if the server crahs and unwritten write IOs are in this cache.

Best regards,
Patrick