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I have inherited what I think is a badly configured VMWare ESXi 4.1 system, I know very little about VMWare. It currently hosts 2 systems. They are both on the same datastore, which is on RAID 5.

  • System A has 44GB of used storage
  • System B has 1.28TB of used storage. Thin provisioned. The guest (Windows 2003 server) thinks it has 1.69TB.
  • The datastore has 0.00B free (!).

The datastore hit zero as system B was growing rapidly. I am migrating services off of System B as fast as I can (and deleting stuff!). I still need it for a while.

The guest now reports it is using around 700GB. It also needs a defrag. The VMWare host does not have the space for System B, if System B zeroes all its blocks: I believe defragging System B should improve its performance, but increase its "used storage". If I delete System A, giving the datastore 44GB, can I defrag system B without system B trying to expand to fill more than the host has, and never booting again?

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up vote 0 down vote accepted

I'm sure this has been asked before here but in general you should defrag your guest OS's the same as you would in a physical server with one exception, when you're using thin provisioning. If you defrag a thin disk it'll just blow it out to its full 'thick' size - one of the reasons why you need to really understand what you're doing before using thin disks.

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I have read elsewhere that defragging a guest will increase the size of a thin disk. But will it really increase it to its full thick size? Can someone who has tried this comment, can someone point me to some documentation? – ColonelFazackerley Jul 6 '11 at 14:03
It will, that's what I said, I know, I've done it and seen this happen (ESXi 4.1, Windows 2008) – Chopper3 Jul 6 '11 at 14:07

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