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I have a ESXi servers (4.1 U1) connected to an iSCSI NAS, where 4 LUNS have been defined and presented to this host; all the LUNs are 3 TB in size. ESXi correctly sees the LUNs and acknowledges their 3 TB size.

I know the maximum size for a VMFS datastore is 2 TB, so creating a single datastore for each LUN would be a waste of space; I also know that creating multiple datastores on a single LUN is not a best practice, and it doesn't seem to work either: if there already is a datastore on a LUN, the vSphere Client just doesn't let me create anything else there, it doesn't even list it in the list of available devices for creating datastores.

I know I can use extents to create a datastore bigger than 2 TB, but this only seems to work across multiple LUNs: when I try to increase the size of a datastore using the same LUN where it resides, ESXi tries to actually increase it, so it won't go above 2 TB in size.

My question is: is there any way to combine two extents in the same LUN, so effectively creating a 3 TB datastore made up by 2 1.5 TB extents?

If this is not possible, is it possible to create two datastores in the same iSCSI LUN? I know it's not best practice, but it should at least be possilbe... but looks like it isn't.

If even this is not possible, then... how to make use of these 3 TB LUNs?

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up vote 4 down vote accepted

You can't do this sorry, not with v4 as it's a limitation of SCSI-2/VMFS3 (version 5 however changes things a lot ;) ). Just go back and represent your LUNs as 2TB one and extent them if required, you're still limited to 2TB vmdk's anyway so it's a little pointless doing extent'ed DS's anyway really. If it's any consolation I limit my DS's to 500GB anyway to ensure the ops people don't over subscribe any given DS with VMs.

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Sad but true... ok, thanks. –  Massimo Jun 10 '11 at 12:33
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