Poor write performance (using local storage)

[carnold-mixing]

I've recently setup my first ESX server (3.5 update 1), after using GSX server for a few years, and write performance in a Windows based VM seems quite poor compared to a physical Windows server (I was aware in advance that there would be a performance hit, but I thought that it would be quite modest ?).

ESX is running on an HP DL360G5 server with four 72GB 15,000 RPM SAS HDD's setup as RAID5 with some Windows Server 2003 VM's, I also have a physical Windows Server 2003 setup on exactly the same hardware.

Using a disk performance tool I like, CrystalDiskMark, read speeds on the ESX VM's are around a third quicker which is nice but write speeds are about six or so times slower (e.g. the VM's have a write speed of 10.77MB/s while the physical server has a write speed of 70.66MB/s).

ESX was installed as is out of the box, no tweaks where made and when the storage was setup in ESX all defaults were accepted.

Without having to re-install ESX (the host is now in a production environment) is there anything that can be done to improve write performance ?. I'm still interested in any advice in regards to the initial setup of ESX on similar hardware though as I'm about to setup another ESX host in a few weeks and this time I'd like it to be tuned to perfection in advance.

Thanks

[BenConrad]

Does your Smart Array P400 have BBWC (Battery Backed Write Cache)? If not, write performance will suffer very badly.

Ben

[carnold-mixing]

Hi Ben,

I'll check all of my HP servers now to see what they have, I'm in a new job I started eight months ago so didn't purchase any of them.

My server experiance is will Dell so I wasn't aware of the BBWC option on a P400 controller, but I am now. I get the feeling that the fast physical WS2003 server I have does have BBWC as it's has two Quad Core Xeons in it and HP state that all models that ship with 2 CPU's have BBWC as standard.

Can you elaborate on 'very badly' ?, half the performance ?, a quarter ?.

Thanks for making aware of this

[BenConrad]

One example, from a long, long, long time ago:

We had a 12 disk Raid-5 on a Proliant storage system, used as a disk-to-disk backup location. Backups were running at around 8MB/s. Adding the BBWC made the backups run at around 32MB/s.

At the time, I didn't know how to use IOMeter, that would have been the ultimate test of before and after.

Trust me, you NEED write cache (with battery backing) so you can take advantage of 'write back' disk IO. The alternative is 'Write Through' and that is slooooooow. Even a small amount of BBWC (64-128MB would make a nice improvement).

ben

[carnold-mixing]

Thanks for the advice Ben.

I found the forum post...

... which ties in exactly with what you've been saying. I'll definately be getting the BBWC upgrade module and cable for my P400 !.