doctormiru
Enthusiast
Enthusiast

General poll about VMFS extends

Jump to solution

Hi all

I'd like to open this poll, because I like to hear different opinions and experiences using VMFS extends with VI 3. There are 2 theories whether to use it or not.

To have it a bit organized please post your answers in the following structure:

  • Are you using VMFS extends?

  • If yes / if no why?, please post also positive and negative experiences

  • To use small LUN slizes in combination with extends or to use multiple larger LUNs?

  • How many VMs do you place on a single VMFS volume?

I'd like to thank you in advance for your interesting posts.

Rgds

Michael (drmiru)

0 Kudos
1 Solution

Accepted Solutions
mcowger
Immortal
Immortal

  • Are you using VMFS extends? NO

  • If yes / if no why?, please post also positive and negative experiences NO, because of performance issues and reservation locking design.

  • To use small LUN slizes in combination with extends or to use multiple larger LUNs? We stripe smaller LUNs on the array side, and present them as 500GB LUNs to the hosts

  • How many VMs do you place on a single VMFS volume? approx 20

--Matt

--Matt VCDX #52 blog.cowger.us

View solution in original post

0 Kudos
8 Replies
depping
Leadership
Leadership

No,

Why? Cause there is no reason to use it at all. You can migrate VM's live to another datastore if a VM needs more diskspace.

Duncan

My virtualisation blog:

0 Kudos
Patrick_Miller
Enthusiast
Enthusiast

extends are evil.....very evil.

0 Kudos
sbrodbeck
Contributor
Contributor

No, not anymore. We went to no extents for two reasons:

1) Performance. We had way too many VMs hitting a single VMFS, to the tune of 20. By reducing it we now have 5 VMs max hitting each VMFS and performance is definitely better.

2) Integrity. One thing that scared us is the possibility of losing the root LUN taking all the data on the other LUNs with it. Now should a single LUN become corrupted, the impact is far smaller.

Our LUNs range in size from 210GB to 900GB range due to hard drive sizes. While we lose some disk space to have free space on each LUN opposed to a group, it was felt well worth it because of the above two reasons.

The number of LUNs varies greatly depending on the VM functions and what we see coming from our internal customers. We have a couple with just 1 VM while we have three LUNs with 5 VMs. We try and anaylze each VM and place it on a LUN with exactly the opposite type of machine. Thus a low disk activity VM will be placed with a high disk activity VM. We have 7 VMs that to one degree or another can hit the disk pretty hard at times. Each one is on a separate LUN.

JDLangdon
Expert
Expert

depping wrote:

"Why? Cause there is no reason to use it at all. You can migrate VM's live to another datastore if a VM needs more diskspace."

Isn't this fuctionality only available with VI 3.5?

Jason

0 Kudos
doctormiru
Enthusiast
Enthusiast

yes you're right, svmotion is only available since 3.5. But it's not all about moving the VMs to other LUNs . The storage management overhead and the performance are very important facts too.

0 Kudos
kjb007
Immortal
Immortal

I prefer to use extents so alleviate I/O on my SAN LUNs.

Our SAN array is loaded with tens of disks to spread the I/O over several platters. Then the LUNs are carved out to reduce I/O on the LUNs themselves, but which are still spread over several platters. I prefer to have one point of storage, centralized for my VMs, and prefer to have a large datastore made of smaller LUN extents. So the I/O is split between the LUNs, but still contained inside one large VMFS volume, which in my oppinion, is getting the best of both worlds, ease of administration and balanced I/O. I get anywhere from 4-10 VMs per LUN, but still on the same large VMFS.

-KjB

vExpert/VCP/VCAP vmwise.com / @vmwise -KjB
mcowger
Immortal
Immortal

  • Are you using VMFS extends? NO

  • If yes / if no why?, please post also positive and negative experiences NO, because of performance issues and reservation locking design.

  • To use small LUN slizes in combination with extends or to use multiple larger LUNs? We stripe smaller LUNs on the array side, and present them as 500GB LUNs to the hosts

  • How many VMs do you place on a single VMFS volume? approx 20

--Matt

--Matt VCDX #52 blog.cowger.us

View solution in original post

0 Kudos
williambishop
Expert
Expert

While this was a good way to go with older arrays(I've got aix administrators who still want to do this until I show them what the disk layout on a decently binned symmetrix looks like), it is no longer valid unless you incorrectly layout your storage device(and you actually have to put effort into messing it up).

Why go through the headache and work to basically do what your controller will do for you, only better? Extents are a pain in the ass, especially if something goes awry. You're much better off laying out your array to do a raid than you are to diy and make a mess of it. It's NEVER as good.

As to the rest of the questions, depending on the system, I might have anywhere from 10 to 150 vm's on a single lun. The luns range from 10G to 2TB, and unless it's a beast, they get a raid 5, 3+1 layout. If it's a beast, I'll move it to a 1-0 cross cabinet setup. I have some seriously heavy hitters(a TB oracle database can do some serious IO)...and I have yet to run into a contention issue.

Ita feri ut se mori sentiat
0 Kudos