Converting Hyper-V VHDs from dynamic to fixed

[Remiel]

Wonder if anyone could offer some advice on a tricky situation I need to resolve.

 

I've recently taken over as NM at a college with a partially virtualised server setup.

 

I've currently got 2 hyper-v hosts with identical specs: Hyper-v-01 and Hyper-v-02 (S2012 R2 Datacenter) Dell PowerEdge 720XDs with 1 MD1200 SAS array each. Host 01 is running two VMs – one running SIMS (S2008 R2) and the other running the local Exchange server (Exchange 2010 running on S2012 Standard).

Host 01 has been setup with three 2Tb RAID 5 arrays, one of which is acting as the C: which also has one of the VMs running on it. I’m well aware that this is a far from idea setup and needs to be sorted as a priority. My game plan is ideally to replicate then failover both VMs to host 02, flatten host 01 and rebuild it with a 250gig C: and the rest as VM storage in RAID 10.

The problem I’m having is that both VMs have been setup with dynamically expanding VHDs. As far as I’ve found, I’m not going to be able to convert the VHDs to fixed size without incurring downtime for the VMs. This isn’t an issue with the SIMS server over the summer period, but I’m very concerned about the exchange server being offline for a prolonged period of time (one of it’s 3 VHDs is over 1Tb).

 

Host 02 is currently empty. I’ve rebuilt the RAID to a single 2.7Tb RAID 10 that has enough space to replicate the two existing VMs on Host 01 across, but I’m not sure it’s going to help yet.

I should say that all servers are currently being backed up via DPM 2012, although the VMs are being backed up at VM level instead of host which is another kettle of fish that needs sorting afterwards.

 

Regarding converting the VMs from dynamic to fixed - Is there anything I can do to mitigate downtime in this situation?

 

Many thanks

[Steve21]

Unless I'm missing something why do you even want to change them to Fixed? As in to migrate across etc can use either so you can sort raid without changing them.

 

Steve

[Remiel]

There were 2 reasons really, the first is that I was under the impression that DPM 2012 cannot do online backups VMs at the host level if any of the VHDs are dynamic (https://technet.microsoft.com/en-gb/library/hh757970.aspx). Am i misinterpreting that though? The second was that running exchange on a dynamically expanding VHD has a negative impact on performance compared to fixed?

[snagrat]

Fixed will give you better performance but are you experiencing performance issues?

 

I backup using DPM on dynamic disks without issue, but will read through that article now!

[localzuk]

Backing up dynamic VHDs is difficult - you may find that your backup appears to have worked, but is actually out of date - with the data being that of the last time the machine was turned off.

 

We moved all our dynamic disks to fixed for this exact reason.

 

I believe 2012 R2 has better handling of this now though - we're still using R1 - but I haven't investigated properly (a job for summer).

 

I don't think there's any way to reduce down time, without your exchange server being in a cluster of exchange servers, so you could take one down and the exchange cluster still operate normally.

[Remiel]

Looks like I'm going to have to plan for exchange downtime then

 

Many thanks for the clarification though!