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What block size to use in vmware datastore

Posted on 2013-06-24
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If I were to create a new datastore on a newly presented LUN and make the block size 1 MB what would happen if I expanded the VMDK larger than 256 GB? It's saying that's the largest file, so would it not allow me to expand beyond that or would it create a second VMDK and allow the guest OS to have a bigger volume?
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Question by:knfitz
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Andrew Hancock (VMware vExpert / EE MVE) earned 500 total points
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that depends on whether you are running VMware vSphere 4.x ot 5.0.

if you set the block size to 1MB on VMware vSphere 4.x, the largest file size (vmdk) is 256GB, people also forget, this includes the snapshot size!

see here

• 1MB block size – 256GB maximum file size
• 2MB block size – 512GB maximum file size
• 4MB block size – 1024GB maximum file size
• 8MB block size – 2048GB maximum file size

so I would set to 8MB, you can then have files up to the maximum of 2TB, there is no performance degradtion, or disadvantage of setting to 8MB and forget about it.

VMware vSphere 5.0 and VMFS-5 does not have this limitation.

Unified 1MB File Block Size. Previous versions of VMFS used 1,2,4 or 8MB file blocks. These larger blocks were needed to create large files (>256GB). These large blocks are no longer needed for large files on VMFS-5. Very large files can now be created on VMFS-5 using 1MB file blocks.

source
http://blogs.vmware.com/vsphere/2011/07/new-vsphere-50-storage-features-part-1-vmfs-5.html
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