VMware Communities: Message List - Importance of local storage performance when using a SAN?

Re: Importance of local storage performance when using a SAN?

zippy_paul — Mon, 23 Jun 2008 14:33:36 GMT

I'm not sure if the question has been answered. we've established that 15kSAS drives are faster than 10k ones... and that you need adequate RAM in your ESX server... and mike did mention that he would use SAS for this purpose, however i didn't quite catch the reason.

and Mike are you saying that you would not use RAID 1 because of the 50% hit?

i've got the same issue. i'm building ESX Servers. we have iSCSI SAN on which i want to store most stuff, however am thinking perhaps it's better if i put the ESX swap file on local storage... in which case, is it worth using SAS? (assuming we're on a tight budget) and if so, why?

Re: Importance of local storage performance when using a SAN?

mattjk — Fri, 21 Mar 2008 01:36:41 GMT

Thanks for the info guys.

Re: Importance of local storage performance when using a SAN?

mike.laspina — Wed, 19 Mar 2008 15:56:47 GMT

Thanks Duncan,

I actually didn't word it quite correctly. Its not a single rotation. It is the number of rotations in a moment of time that gives it more read/write I/O.

But regardless the result is the same, significantly better performance.

Re: Importance of local storage performance when using a SAN?

depping — Wed, 19 Mar 2008 15:50:04 GMT

Good call mike! 6 or 4 is a huge difference indeed.

Duncan
My virtualisation blog:
http://www.yellow-bricks.com

Re: Importance of local storage performance when using a SAN?

mike.laspina — Wed, 19 Mar 2008 12:07:47 GMT

Hello,

Yes there will be a big difference. The reason a 15k is faster than a 10k is the number of reads and writes that can occur on a single rotation of the platter. For example in one rotation moment on a 15K we get an arbitrary 6 writes this will equal 4 writes on a 10k drive. This is 50% better per rotation time . What you need to consider is do you really want to use local SATA disk. We normally do this to prevent heavy swap I/O over the SAN. You can prevent this by using the correct memory resource on the host. I have almost not vmdk swapping and I don't have any local disk, it all boot from SAN. The other thing to think about is RAID 1 will cost 50% on every write operation, this will not be optimal for a swap vmdk. Ram and tuning is the correct way to deal with these issues.

p.s. I would chose SAS over SATA for this purpose.

Message was edited by: mike.laspina

Re: Importance of local storage performance when using a SAN?

weinstein5 — Wed, 19 Mar 2008 11:48:33 GMT

I have not seen much of a difference inn the overall performance of your ESX hosts - there will be a slight performance increase in the Service Console just basedon the imptoved performance of the swap space fir the service console - this of course is assuming is all you VMs being stored on some NAS/SAN device -

Re: Importance of local storage performance when using a SAN?

mattjk — Wed, 19 Mar 2008 08:39:00 GMT

Bump.

Anyone?

Re: Importance of local storage performance when using a SAN?

mattjk — Tue, 18 Mar 2008 05:16:47 GMT

Yep I already know that much - at least RAID-1 is a given. My question is regarding whether the performance of local storage affects the overall performance of ESX significantly - i.e. is there a big diff between using 2 15k SAS disks vs 2 7.2k SATA disks?

Re: Importance of local storage performance when using a SAN?

weinstein5 — Tue, 18 Mar 2008 00:59:12 GMT

you are correct - RAID-1 shoudl be fine for the local disk - it is used by the Service Console including SC swap file -

Importance of local storage performance when using a SAN?

mattjk — Mon, 17 Mar 2008 23:33:06 GMT

Hi all,

How important is the performance of local storage when storing all VMDK's on a SAN - i.e., the local storage is only used to store ESX Server itself (and I assume provide swap disk, etc)?

RAID-1 is a given for redundancy, but beyond that? Is there going to be any appreciable difference in real-world ESX performance between 2-disk RAID-1 7.2k SATA and 2-disk RAID-1 15k SAS?

Thanks.