Hyper-V guest using up all disk space on host

[johnhugh]

Hi,

I run a Windows Server 2008 machine with Hyper-V role installed.
On that machine we run 2 guests, both with Win Server 2008. One guest acts as a file server, the other is an application server running SQL Server 2005.

There is 10GB of free disk space left on the host. It has happened now a couple of times that mysteriously these 10GB were used up completely causing all guests to stop.
Both guests themselves have still got ~20GB free space available. The disks do not grow dynamically.

Previously I used snapshots and it appeared the snapshot grows with time. Especially when running a SQL Sever backup.
However, I've deleted the snapshot now and still have the same problem.

Anyone else experienced that before?

 

[kmcferrin]

This is correct, snapshots do grow with time. The way that they work is that a differencing disk a created, and all new data written to the VM's disk is written to the differencing disk, as is all data that changes. The original VHD file is essentially locked in read-only mode, allowing you to roll back. However, the differencing file starts small and will grow as more changes are written to the VM's disk. You could have a VM with a 20GB disk attached that actually consumes several times that much space, especially if you are using multiple snapshots, and the longer that you use them the bigger they will get.

Have you looked to see what is consuming the free space on the host? If you do not have dynamically expanding disks AND you do not use snapshots then it's possible that something else not related to Hyper-V is using the disk space.

Also, what are you using to backup the VMs? Something like SCDPM will make use of VSS and snapshots to take VM backups, so it's possible that the space is consumed during backups, the backups fail, and the space is not released.

________________________________________
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[johnhugh]

Hi kmcferrin,

Thank you for your reply!

Snapshots in Hyper-V seem to work different as to what I'm used to in VMWare. A snapshot in VMWare is really just a snapshot of the life system I can revert to. I continue working on the live system while my snapshot just sits there.

It's hard to tell what is taking up the space now as I only ever find out once it's too late and all space has been consumed. I'll have another go.

When I mentioned backups I was just talking about SQL Server backups on one of the guests.