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dougdavis22
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Correct 'size' for 2TB LUN for ESX

I have the need (on occasion) to provide a VM with a 2TB VMDK. In order to do this, I obviously need a 2TB LUN with a VMFS on it.

My question is, what it the correct size in GB that I should present to ESX to ensure that (a) ESX will see it OK and (b) I can get as close to a 2TB VMDK as possible?

We have managed to get a 2048GB (real 2TB) LUN visible to ESX, but have had to format it at the command line as the VI Client didn't like it.

Any suggestions appreciated.

Cheers,

Doug.

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DougBaer
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The max LUN size is actually 2 TB - 512 bytes -- this is due to a 32-bit addressing limitation and overhead for VMFS bookkeeping.

You will definitely want to check out this article.

http://virtualgeek.typepad.com/virtual_geek/2009/06/vsphere-and-2tb-luns-changes-from-vi3x.html

It applies to vSphere, but good information unless you want to mess with your storage during an upgrade.

Doug Baer, Solution Architect, Advanced Services, Broadcom | VCDX #019, vExpert 2012-23

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DougBaer
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The max LUN size is actually 2 TB - 512 bytes -- this is due to a 32-bit addressing limitation and overhead for VMFS bookkeeping.

You will definitely want to check out this article.

http://virtualgeek.typepad.com/virtual_geek/2009/06/vsphere-and-2tb-luns-changes-from-vi3x.html

It applies to vSphere, but good information unless you want to mess with your storage during an upgrade.

Doug Baer, Solution Architect, Advanced Services, Broadcom | VCDX #019, vExpert 2012-23
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mike_laspina
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Hi,

All VMFS volumes have metadata files. These files are required. You must at a minimum leave some space on the volume for metadata. I would suggest 2GB at the very low end since only 1 vmdk will be present but 4GB is more appropriate.

Thus allocate 2044GB to the vmdk as a maximum.

Regards,

Mike

I have used 2048GB as a value successfully for the LUN.

vExpert 2009

Message was edited by: mike.laspina

http://blog.laspina.ca/ vExpert 2009
dougdavis22
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So, based on your information of 2TB - 512 bytes, that is equivalent to 2199023255040 bytes which actually equals exactly 2048GB, yes?

This would mean that, if I ask my SAN guys to give me a 2048GB LUN I can then format that happily with VMFS and put a VMDK up to, say, 2044-2046GB on it with no problems now or in the vSpehere future?

Doug.

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mike_laspina
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I would be careful, maybe use 2047GB as the LUN size to prevent a vSphere issue.

vExpert 2009

http://blog.laspina.ca/ vExpert 2009
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DougBaer
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We generally request 2047 GB as the max LUN size from our storage folks, if we're looking at datastores that big. I've normally opted for datastores of no bigger than 500 GB, though, to reduce the number of guests per LUN and restrict I/O contention, but if you need big LUNs, you need big LUNs. Smiley Happy

Doug Baer, Solution Architect, Advanced Services, Broadcom | VCDX #019, vExpert 2012-23
dougdavis22
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Thanks guys - I think 2047GB sounds like the safest option.

Doug.

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