What's the latest on LUN sizes?

[REALM]

What's the best supported lun size for 3.5? I'm using 400GB now because my rep told me a while back that one day converting to vmfs4 if/when that came around may be a problem based on what he saw in the vmfs2 to vmfs3 conversions.

Thoughts? I would like to use 1TB luns.

[lamw · Accepted solution]

I believe they're still the same in ESX 3.5 Update 1/2

Take a look at:

If you need a break down for the different block sizes, please refer to:

Though I believe 2TB is still the limit

Also the new VMFS version in Update 1 / 2 is 3.31 and I would assume that VMware would ensure that whatever size LUN you chose that if a new VMFS version came out it would not hinder performance, one would hope. Or they could assume if the change is greatly different, that a Storage VMotion would take care of that fact vs trying to upgrade the underlying VMFS volume version, but I think you should be okay with future release of VMFS versions.

[weinstein5]

2 TB is still the limit for the LUN size -

[TomHowarth]

As you probably know VMFS size is based on block size therefore

1MB Block = 256GB MaximumVMFS Size

2MB Block = 512GB Maximum VMFS Size

4MB Block = 1024GB Maximum VMFS Size

8MB Block = 2048GB Maximum VMFS Size

thereforet the maximum VMFS partition is 2TB, this just happens to fit nicely with the maximum addressable LUN size as well

Tom Howarth

VMware Communities User Moderator

[dtnvm]

Tom,

sorry to correct you but although the VMFS size does depend on block size this is only interesting for very big volumes. As stated in the storage maximums section of the VI3 docs, block size of 1 MB restricts the VMFS volume size to ~50 TB while all other block sizes give a max VMFS size of 64 TB but this will require the use of extends. A VMFS on one single LUN is restricted to 2 TB regardless of the block size since the max supported LUN size is 2 TB.

The block size will mainly affect the maximum file size of a single file on VMFS (1 MB blocks = 256 G, 8 MB blocks = " TB).

Regards,

Jan

[TomHowarth]

Good point, I should have been more exact in my answer

Tom Howarth

VMware Communities User Moderator

[wpatton]

REALM,

As I personally was very badly burned by VMWare on the VMFS2 to VMFS3 block size changes, I had to "convert" (i.e. format and restore) almost 60TB of datastores from 16MB to 4. I have stayed completely away from 8MB block size, and stuck to only 1, 2 or 4.

I now recommend this at all times to try to future proof against VMWare.

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[REALM]

Can someone fill me in on the block size thing? When I formatted my vmfs3 luns, all I did was use the VC gui to create a datastore. Where can you check block size used and how can you change it?

Thank you.

[lamw]

Please refer to this document for all your questions:

Block sizes determine the size of your VMFS volume

1MB Block = 256GB MaximumVMFS Size

2MB Block = 512GB Maximum VMFS Size

4MB Block = 1024GB Maximum VMFS Size

8MB Block = 2048GB Maximum VMFS Size

[wpatton]

Checking your existing block sizes can be done by opening Configuration Tab -> Storage

Select the datastore in question and it will show you the properties of the datastore and the block size. Changing it however is not possible without a reformat and loss of any data on that datastore.

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[REALM]

Excellent... thank you, I had no idea about this and just formatted 8 new luns. Doh!

Good to know for the next 8 that are coming.

What happens if I have a 1MB block size volume with VM's on it, and I want to move them to a 4MB block size volume lun? Will that work going forward at least?

[lamw]

As the previous poster stated, any changes to the block size will require a reformating of the LUN and LOST of data, including VMs. Your best bet is to power them off and copy them to another newly created LUN of the right block size OR if you have to keep VMs running, do Storage VMotion to another datastore of which can be (iSCSI/FC SAN, NFS or Local Storage) long as you have a VMotion license and Virtual Center and RCLI installed.

[wpatton]

You will be fine, you can Storage VMotion or Cold Migrate any disk between any of the VMWare supported block sizes. 1, 2, 4 or 8.

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