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virtualfish321
Contributor
Contributor

Maximum RAW Disk size?

I'm having a time trying to figure out what the largest RDM disk is that I can create for a VM.  At first, I created a 2.8tb volume on the san, and of course when I tried to add it, it was rejected saying that the vmdk is larger than the maximum size supported by the datastore.  So, I double-checked the datastore settings, and with some reading found that using an 8MB block size for your datastore should allow a maximum RDM of 2tb.  At that point I deleted the datastore, created it with 8MB block size (total size of the datastore is 56gb), and resized the RDM to 2tb.  I went back to readd the RDM and I still get the error that it is too big  for the datastore.

So, what's the biggest I can use here?  I really want at least a 2tb volume, as this is for a storage NAS I'm building.  Seems silly that if you're using an RDM you're limited to the datastore that the machine is running on.  I understand why, but still seems silly.

Anyways, if anyone can help I'd appreciate it.  Thanks!

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6 Replies
mcowger
Immortal
Immortal

In vsphere 4, you are limited to 2TB (minus 512b).

In ESXi5 you can do up to 64TB

--Matt VCDX #52 blog.cowger.us
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virtualfish321
Contributor
Contributor

Thanks for the reply.  So if I created the RDM to be 1.9tb it should work?

Thanks!

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mcowger
Immortal
Immortal

Yup.

--Matt VCDX #52 blog.cowger.us
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virtualfish321
Contributor
Contributor

thanks!

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Dynamax
Enthusiast
Enthusiast

your maximum is 2TB -512. You will probably be able to create a 2047GB LUN on your array as array vendors use standard SI which means TB = 2000GB and VMware uses binary so when they say 2TB max, they mean 2048GB

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a_p_
Leadership
Leadership

Seems silly that if you're using an RDM you're limited to the datastore that the machine is running on.

This limitation is most likely due to the SCSI-2 limit explained at http://kb.vmware.com/kb/3371739 which existed in ESXi versions prior to ESXi 5.0

The maximum size of the RDM you can create also depends on whether you want to be able to use snapshots on this RDM (virtual mode RDM) or not (physical/pass-trough RDM) With pass-trough RDMs you can configure the maximum LUN size (2TB minus 512 bytes). With RDM's in virtual mode you need to "reserve" some space for the snapshot metadata and therefore the maximum LUN size must not exceed 2.032GB (see table "Calculating the overhead required by snapshot files" at http://kb.vmware.com/kb/1012384)

André

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