Creating virtual hard disks–the slow way

Creating virtual hard disks–the slow way

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Over the weekend I reconfigured one of my main servers.  As part of this process – I had to make some large fixed virtual hard disks (800-1600GB in size).  This took a long time…

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I spent quite some a while looking at this screen…

In the past I have talked about why this takes a long time and I have also talked about a tool that is available that can make fixed virtual hard disks quickly.  So you may be wondering why I would still create virtual hard disks the slow way.

Well – there are two reasons:

  1. Support.  I know that all of our testing is done using virtual hard disks created by Hyper-V – not by any other tools.  This means that I can have high confidence in the fact that I am unlikely to have problems with these disks – and that if I do have any problems, we will fix them.
  2. Reliability. I like to know that every sector of the disk has been touched before I put it into production.  For the same reason, I always do a full (not quick) format of a disk before putting real workload on it.  I have personally had the experience of having a system where everything appeared to be fine – but creating a 200GB fixed virtual hard disk (the slow way) would cause the system to crash; which in turn revealed that there was a bug in the disk driver I was using.

In my opinion – when it comes to production systems, sometimes it is just worth taking the time to do things properly.

Cheers,
Ben

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  • FYI: A slow format just calls VERIFY10/16 on every sector. It doesn't even write data... At least, that was the case when I last checked.

  • Simon - correct, but a slow fixed VHD creation does write to each sector.

    Cheers,

    Ben

  • I would agree to the argument in favor of reliability. If this is taking a long time does it make sense to make it something running in the background? So as an admin I can put requests in to prep these monster vhd's in advance and check back on the status from time to time. Given the version of Hyper-V is going to support larger disks this is only going to take even longer ;-)

  • blogs.technet.com/.../use-powershell-to-create-vhds-for-hyper-v.aspx

    The Hyper-V UI is all WMI driven, I use a back door to create all of the disks, and you can run this overnight, etc. ahead of time, instead of waiting for the VM Wizard to do the work.

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