We wrote a tool called virt-resize last week to resize virtual machines. To get it out the door in 3 days we punted on some hard features.
Nevertheless, I’m getting good feedback on virt-resize from customers. They like it, and it seems it solves a problem that a lot of people are having.
In the coming week we’re going to try a quick 2.0
rev of virt-resize. So, what features would you like to see? Here’s the manpage for the current version. At the moment it only resizes partitions, and leaves resizing the filesystems / PVs / LVs inside them up to the user.
Expanding filesystems automatically?
Do you use LVM inside your guests?
Are Windows guests important to you?
Do you ever need to shrink a VM?
Richard WM Jones 
Expanding filesystems automatically?
Not generally needed. Doing it on boot is pretty trivial.
Do you use LVM inside your guests?
Yes
Are Windows guests important to you?
Nope
Do you ever need to shrink a VM?
Don’t think I ever have.
All of my Linux VM’s (~100 at the moment) are trending towards having no partition table at all (no boot sector, external kernels w/ Linux). It makes management quite easy since a given image can simply be mounted loopback without libguestfs or kpartx.
No LVM inside guests unless it’s being used for training/development purposes. Even if a given installer slips it in, I’ll remove it after the installer is done (move files to a new image).
Automatic expansion could be interesting for file-based images. ~60 of my VM’s are on ext3 rootfs sparse file-backed volumes on an NFS server. Another dozen or so are ext4 on LVM LV’s, but that will grow to 400+ in the next 3-4 weeks. Almost all of them are using KVM virtio disks. The few OpenSolaris, FreeBSD and Windows VM’s are typically IDE, except for the 2-3 Windows VM’s using the Windows virtio drivers (which are working fine).
Windows guest support is probably the most complex to handle, so every tool to help with that is a boon. I’ve made due thus far with fdisk/kpartx/ntfs-tools.
I’ve never shrunk a VM (on purpose).
… but with root. libguestfs will let you view these without needing to be root. There is also a security issue here: I hope you trust all your VMs before you mount their disks as root on the host.
I’ll agree though that avoiding partitions / legacy boot process entirely is a Good Thing.
Automatic filesystem expansion would be a useful time-saver, though shouldn’t hold up more important features, such as (for me) LVM and Windows support.
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