Firstly, go and read this article:
http://www.enterprisestorageforum.com/sans/features/article.php/3844426
It discusses the merits of defragmenting SAN based disks. With the heavy usage of SANs within the VM sphere, it makes it particularly relevant.
OK, done reading? I’ll continue…
After deploying a new VM yesterday, from one of our Windows 2008 R2 64bit templates, I noticed the new Task Scheduler. I was having a bit of a poke around and noticed that by default there was a scheduled task to defrag all its “local” disks at 1am Wednesday every week. Now this task is disabled, but be careful about enabling this in your gold template.
Besides your personally thoughts on the need to defrag SAN disks, imagine all your VMs running on a SAN decide to defrag all their disks at the same time. Yikes! Hopefully Microsoft put in randomization on the day and time during the night these things are set, when the OS first installs or during sysprep. However it doesn’t appear so.
You never want to defrag a VM that has a snapshot.
What you don’t like it when your snapshot merge take 4-6 hours? 😉
The defrag task has been there since early builds of Vista and was originally set to run at Sunday 4am, but they moved it to Wednesday 1am based on feedback during the beta. Its continued to be present in every Windows release since then, but disabled by default for server O/S’s.
As for someone enabling it across all their VMs, well let’s hope their SAN isn’t busy at 1am Wednesday’s – because it’s about to be brought to its knees! And then the storage admins are going to come looking for those pesky VMware admins… 😉
i have done a clean install of win2008 standard sp1 and win2008 standard 64bit sp2. both have this task enabled by default.