| Chris,
The SATA arrays will always poor IO performance in environments like yours. I have some experience from going through issues with an 8-core Postgres server with heavy disk IO problems.
SCSI Raid will be better, especially if you have alot of spindles. Raid 10 instead of Raid 5 etc.,. And if you split it up across both channels of a dual channel card or spit it across multiple cards, that will help too. Problem is size limitations of SCSI raid 10 due to the numbers of drive slots in most external enclusores. 14-bay enclosure with Raid 10 and 146Gb drives will give about 1Tb. I wouldn't recommend using the 300Gb scsi drives. Smaller the drive, the better.
Eventually, SCSI will also break down. When that happens, you'll start to need a Fibre-Channel attached SAN, one specifically designed for high IO environments. The EMC Clarrions are getting a little better in price, but still pricy when compared to SATA arrays.
You may never need the EMC-level performance, so SCSI Raid with alot of spindles and good HBA controller management might do the trick for awhile.
-John On Sep 14, 2007, at 10:50 AM, W. Chris Shank wrote: I need to spec-out and architect another VMWare and/or Xen VM host server. Currently I have one with 8 cores, 4GB ram, and 1.5TB HDD as 4 500GB SATA with hardware raid5. We are starting to hit the wall with this setup running 5 VMs on it. Particularly, it seems the HDD I/O is the bottleneck. If one VM hits the disks hard it makes the others pretty much useless.
So I have a budget to get another honking server. I'm confident the quad-core Xeons with the vm extensions are sufficient. I'll go ahead and bump the RAM to 16G too. The area I'm most concerned with is the disk I/O. I'm thinking that instead of one big RAID5, I'll pair smaller drives - so i'll have 4 sets of 2 250G SATA mirrors. Then direct it so that 2-3 VMs are on each raid. Or should I go SCSI and keep one large RAID5?
So if you had the $$, what would you get and how would you configure it.
Thanks
--
W. Chris Shank
ACE Technology Group, LLC
www.myremoteITdept.com
(610) 640-4223
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