Strap on your geek safety belts: here comes a buzzword-laden post.
When I got my work laptop I promptly installed Ubuntu Lucid Lynx on it, choosing to add the new Linux filesystem, ext4. Over the course of using my laptop I have seen mysterious slowdowns, where the disk I/O seemed to grind to a halt.
This was particularly evident in my virtual machine sessions, which have the characteristic of doing lots of reads and writes from one or more large files. I use QEMU to run a virtualized Windows XP session for the few applications I can’t use in Linux (cough GoToMeeting cough). Whenever Windows installed its numerous patches the system would grind to a halt. Same thing for installing a CentOS guest VM: what normally would take 20 minutes began to take 40 hours.
It was obvious something was broken somewhere. I had a little-used partition on the drive, so I opted to do an experiment. I would reformat the partition using the tried-and-true ext3 filesystem and try running my VMs off of that.
Like magic, the horrendous slowdowns ceased! Where before the system was spending 40% or more of its time in a wait state, now it hardly cracked 5%! My CentOS install went blazingly fast, as expected, and Windows no longer crawls along.
I had read rumors on the Internet that ext4 had caused others some trouble but discounted those rumors until today. Now I’m stripping ext4 off the rest of my partitions and going back to ext3. It’s obvious to me that ext4 doesn’t meet my needs.
You could always use a real filesystem like XFS. O:-)
Good idea! Yeah, I’ve used XFS for my media servers and like it very much. I haven’t considered using it for a VM server, though. I’ll give it a try and see how the performance is affected.
I’d be interested to hear those results!
I saw something recently that advised against ext4 on the filesystem that contains your VM disk images… I forget where… I think it might have been a warning from VirtualBox itself. So while I use ext4 on most of my filesystems, I use ext3 on the one where my VM’s live.