2013-03-28 02:30 AM
it may seems a silly question, but I've been looking for an answer for some times and didn't find any document that answer to this question. I see also on several forums that I'm not the only one asking for this question.
What is the favourite lun type for San Boot of ESX/ESXi server (in my case version 5, but I guess any clue for other version would be great).
My guess is that the linux lun type would be the good one (since it's not datastore luns) but i can't find anything in NetApp docs, TR, kb that confirms this.
Another question (depending on the answer for the previous one) is:
My customer already installed ESX on luns with vmware type. Should he reinstall it or can it run like that without a problem ?
2013-03-28 11:20 AM
Yes, this is known. One of the partitions that ESX creates is misaligned. Since it is a single partition within the LUN it is impossible to correct. However after boot ESX rarely ever touches these LUNs so I would not worry about then generating Misalignment.
2013-03-29 01:29 AM
Yes, you're right. That's why I ask.
And the following thread from the NetApp support Community states that Linux would be the good choice for ESX Boot from SAN luns :
What I understand from the readings I had since yesterday is:
- vmware lun type is for datastores and when applied to system boot luns, there is misalignment. But it can be choosen for boot luns.
- linux lun type would fit well but it's not stated anywhere in the docs.
- Anyway, misalignment on boot luns should not be an issue since there is no heavy load on these luns.
Am I right ?
2013-03-29 07:40 AM
Misalignment can affect the performance of all of the disks in the aggregate since the misaligned I/O is across all of the disks in the aggregate. You can see how the disks are performing by running:
(wait 10 seconds)
You may have to run 'priv set advanced' or 'priv set diag' to see these commands, don't forget to run 'priv set' to end advanced or diag mode.
2013-03-29 07:43 AM
That is what I heard from several NetApp SEs however I could never find anything relevant in the available documentation. Technically there is not a lot of IO going to these LUNs but I can see how it could impact overall performance of the aggregate.
2013-03-29 07:50 AM
The disk reads have to work twice as hard. ONTAP reads in 4k blocks so if some if the 4k blocks are misaligned you'll have to read 4k blocks twice for every one 4k block read doubling the work done on disk because the 4k blocks are written, for example, 2k in the first 4k block and 2k in the next 4k block. Depending on the misalignment this would impact every disk with misaligned data on it in the aggregate.