I knew about increasing the size (we do that quite regularly) but it is the 
first time I hear about sdelete in conjunction with kvm. I also did not yet run 
defrag inside of windows since I am not sure how each sector in windows maps to 
the underlying zfs volumes. Since they are ‘virtualized’ there might not be a 
1-to-1 mapping anyway and a reorg might make it less fragmented inside of 
windows but have potentially bad effects on the actual physical zfs. 

From: Ian Collins
Sent: Wednesday, January 18, 2017 09:25
To: [email protected]
Subject: Re: [smartos-discuss] 'Defrag' a KVM disk

On 01/18/17 08:31 PM, Matthias Goetzke wrote:
We have a machine which temporarily got 98% full and the boot time of a KVM 
windows server has gotten quite extreme (minutes on the black part of the boot 
alone).
Apart from over-allocating, we guess it might have to do with fragmentation of 
the underlying C drive (just a hunch due to the number of writes on C and the 
fact that overall fragmentation was temporarily >78%) since another win machine 
still booted up quite quickly.
 
If a kvm disk were just a file then I could just make a copy of the C drive (I 
have enough space now) into a new file which should (in theory) just create new 
aligned blocks and once I delete the old file it should be defragmented mostly.



A KVM disk is a sparse provisioned zfs volume, not a file.

Part of the basic maintenance I perform on Windows KVMs is well documented here:

https://www.maketecheasier.com/shrink-your-virtualbox-vm.

You will see the REFER number for the volume reduce dramatically when you run 
sdelete.

It is also fairly easy to increase the volsize of the underlying disk and 
expand your windoze partition to fill it.

-- 
Ian.
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