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How To Increase The Blocksize On A Vmware Datastore

Had a problem with a client who was backing up VM`s with Veeam, the issue was that it could ot backup one of the VMs because of the4 block size on the datastore. So we had to increase this block size on the vmware datastore. We had to storage vmotion the vm to another datastore then do the following. We had to delete the datastore then recreate with the correct block size.

First we select the datastore in question ( make sure it is empty before hand by right clicking it and selecting browse ).

vmware datastore

We then right click the datastore in question and select delete to delete the vmware datastore. AGAIN MAKE SURE THAT NOTHING IS IN THE FOLDER!

Delete vmware datastore

The refresh the vmware storage view to make sure the datastore has gone.Once refresh select Add Storage.

refresh vmware storage

We now select the vmware Disk/LUN and click next.

add storage in vmware

We now select the SAN where the lun is created that vmware will store its datastore on.

select vmware san

VMware will now confirm the location of the LUN on your SAN or storage device.

vmware lun

Now give a valid name to your new vmware datastore.

vmware datastore name

Next the important part, we need to slect our vmware datastore block size, this block size determines the maximum size you create for a virtual hard disk.Check the table below before selecting

VMware Block Size Restrictions

Block Size
Largest virtual disk on VMFS-2
Largest virtual disk on VMFS-3
1 MB
456 GB
256 GB*
2 MB
912 GB
512 GB*
4 MB
1.78 TB
1 TB*
8 MB
2 TB
2 TB minus 512 B*
16 MB
2 TB
Invalid block size
32 MB
2 TB
Invalid block size
64 MB
2 TB
Invalid block size

change vmware block size

Once done you will see the summary screen, click finish then you will have re-sized your vmware datastore block size. If you need to move your virtual machines back with storage vmotion you can now.


Allen White

Allen is an IT Consultant and holds the following accreditations. MCSA, MCSE, MCTS, MCITP, CCA, CCSP, VCP 4,5, 6 and HP ASE, AIS - Network Infrastructure.

Comments (2)

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    Luis Mendez


    This article helped me to solve an issue that I had, thank you very much Allen 🙂


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