Thursday, August 19, 2010

Success in improving RAID speeds

After a long and hard trial process, I have increased the speed of my RAID5 array on an IBM ServeRAID-6M to a very acceptable level

Before I worked on this, guests on a 5 disk RAID5 were getting 5MB/s and after-wards I am getting the following Speeds

  • Windows 2003, 12GB, Read tests with HD_speed are 92 MB/s
  • Ubuntu 9.04 server, 8GB Read+Write tests, using dd are 32 MB/s
My second RAID was only 3 disks because I had a problem with 2 of the disks. Here are my suggestions for building a RAID5 from used parts

  • Test the READ and WRITE speeds of each disk by itself. I had 1 U320 disk that was reading fine at 60 MB/s but crippled down and would only write at 5 MB/s
  • Have the same interface; one disk was a U160, and it could only read at 50 MB/s
  • Do not include any disks that are considerably slower than others, it will slow down the whole array.
  • Not sure this is true with all Array controllers, but make sure that both the disks and the array are set to write back, not write through. Also the setting for the disks can only be change while they are not in an array, and cannot be change once they are built into an array
These are my preferences, and not sure they will affect anything.

  • When building the array use the largest stripe size. The ServeRAID-6M goes up to 64K
  • When formatting the VMFS Datastore choose a larger block size like 4MB or 8MB.

Tuesday, August 17, 2010

ESXi on USB - Part II

I have been working with a test version of ESX 4i, 4.0 U2 on a USB stick. I installed it the USB stick like I documented on my August 4th post. I like it but seeing some problems. For some reason it is slowing down my system. When I benchmark my ESX host it is only getting 5MB/s on disk access for the guests.

Now these guests are either on a single SCSI U320 disk attached to a ServeRaid-6M, or in a RAID 5 config on that same card, and they are behaving poorly.

I believe that somehow the ESX hypervisor is writing to the USB stick and slowing the whole system down. So I am going back to an installable version on a SCSI disk

Wednesday, August 4, 2010


I found this great little tutorial on how to install ESXi onto a USB stick. I know that there are a bunch of ways, but this was fast, simple, and can be done from windows with tools that I already have: WinRAR and WinImage

Give it a shot.

UPDATE: I use this on a dedicated system so I am not concerned with data loss, but from my tests with 4.0 U2 the hypervisor will grab a partition and format it with VMFS.