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VMware and disk partitioning within LUNs

Hi Guys,

We have recently purchased a MD3200 storage array which has 7 disks each 600GB.
We created a Disk Group with 6 disks in RAID 6 (leaving 1 Hot Spare)  giving us a total of 2200GB.

Now obviously we are going to create LUNs for the different VMs.
Now in the past with physical servers I always create partition for Operating System (C:\ drive), partition for DATA (D:\ drive) and partition for Exchange (E:\) as it is good for performance.

In this case we are going to have 3 servers. One a DC running Server 2012, one a Exchange 2010 server with 2008 R2, one Server 2012 to run SQL Server.

Lets say with the exchange server VM now I want to have 3 partitions as above, then should I create partition within the SAME LUN or should I use a different LUN for each of these partitions to get performance benefits.

Please let me know what the best practices say and back that up with some links if possible.

Thanks in advance.
Avatar of Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
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The LUNs and all the virtual disks you create will ALL be on the same  RAID 6 raid group on the SAN, as for performance, there will be no difference, splitting OS and Data onto different virtual disks, and different LUNs, as all LUNs occupy the same RAID group.

However, you may want to split the total RAID group, into smaller LUNs, e.g. 500-800GB, and present to ESX server.

Do not use partitions on disk, but use individual virtual disks, it makes expansion easier in the future, if you use disks, rather than partitions in the VM.
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ASKER

As far as MD3200 is concerned. Virtual Disks and LUN is the same thing.

Yes, I understand there will be no disk performance increase but having OS and data on different partition is beneficial, isn't it?

I cannot create 2 Disk Groups (RAID) as we do not have enough capacity, so that is not an option.

Lastly are you saying "Not to partition within the LUN", but instead "creare a LUN corresponding to each partition" rite??

For some reason DELL PRO support team told me create 1LUN and then have partitions within so that it is easier to do VSMotion etc. What do you reckon?
create a LUN, store virtual disks in that LUN, use single partition on an entire disk.

not sure what Dell are talking about here.
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ASKER

So what you are saying is C:\ drive(OS) = 1 LUN, D: drive (DATA) = 1 LUN, E:\drive (exchange) = 1 LUN? Am I correct?

Also are there still benefits of using partitioning?

I was reading somewhere and someone suggested to use RDM for Virtual Disks?
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Avatar of Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
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ASKER

Aha.. Got you now. So many terms that it gets confusing. Apparently DELL also calls their LUN, Virtual Disk.

So this is what I am going to do -

VM1 = Will sit on LUN1 , and 3 vmdks on it for OS, Data and Exchange
VM2 = Will sit on LUN2, and as many vmdks as required and so on.

Also, I am just curious why you don't think its better to have each vmdk (OS, data, exchange) on it's own LUN?
yes, sorry, that's correct, LUNs = Virtual Disks.

You can use multiple VMs on a LUN, but keep the numbers down.

But do not stack all your VMs in a single LUN, because if the LUN gets corrupted you will lose all your VMs.
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ASKER

I am sorry to ask again but you managaed to confuse me by going back :)

So I create 1 VM per lun but have all vmdks associated with that 1 VM within same LUN. Rite?
Yes, that's correct.

it's entirely up to you if you have 1 VM (all it's files and virtual disks) per LUN, or multiple VMs per LUN.
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ASKER

I will probably stick to 1 LUN per VM atleast.
Also, out of curosity I wanna ask why you don't suggest a LUN for each partition?
you can use a LUN for each virtual disk (with a single OS partition), but you will see little performance gain, in your configuration, because ALL LUNs are stored on the same RAID 6 volume
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ASKER

ok thanks. I though there would be some benefit, but I think you are correct.
there would be a benefit, if you had

LUN1 - RAID 10
LUN2 - RAID 5
LUN3 - RAID 6

but most large SANs are all configured at the same RAID-DP level, all x hundred disks, and to be honest with you the more disks in a stripe the better the IOPS
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ASKER

True, also I am using VEEAM backup and Replication v 6.5, so you don't think there will be any performance benefits whichever way I go.

If you don't know Veeam, it does snapshot based backups.
Yes, I know Veeam!!!

No performance benefits.
Originally LUNs were a physical device on a SCSI bus, typically a disk or tape drive, then along came RAID controllers and layers of virtualisation were added. In a traditional RAID controller several disk spindles are aggregated together (the exact details dependant on the RAID level in use) and a virtual drive is produced, this virtual drive can be presented to a host, either as a) one LUN or b) sliced and diced and presented as multiple LUNs. In RAID controllers like the EVA and 3PAR there are additional virtualisation levels between the individual spindles and the presented LUNs.

Of course at the OS level there is more virtualisation, LUNs only used to contain one partition, now they routinely hold two or more and of course software RAID can be configured on top of this.

And then there could be a Hypervisor like VMware on top of that

So what this means is that a single windows drive letter could be sitting on 5 or more levels of virtualisation!
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ASKER

question not abandoned. I am yet to test this. Please be patient.
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ASKER

Thanks for your help. Additionally I found that for Veeam snapshots you need to keep quite a bit of additional space on the datastore (LUN) or else backup fails