So I was looking through a datastore and was Storage vMotioning a few VMs and it was taking ages. After digging around I noticed that the datastore was mapped across 2 extents.

extenst_3 extenst_2 extenst_1

extenst_3 extenst_2

There should be no reason for this, esp when using VMFS5. After digging around in Compellent by looking at the LUN ID and the naa ID, I found out that both extents were on different Compellent SANs! I have no idea how this came about, but the only way I know of to fix it is to actually, Storage vMotion everything off it to a new volume/datastore, unmount the old datastore and detach the extents.

extent3 extent6

Somebody must have done that in error when trying to extend datastore space. The second extent was labelled as belonging to a totally different area/volume. So how it exactly came about I have no idea.

But it is my job to fix it!

Also VMware did a good blog post on extents and the many misconceptions on then:

https://blogs.vmware.com/vsphere/2012/02/vmfs-extents-are-they-bad-or-simply-misunderstood.html

Misconception 2 is interesting as I was discussing with someone recently too, I have heard it a few times.

Nice to get it cleared up.

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