Fedora and LVM [LWN.net]

Fedora and LVM

Posted Nov 1, 2012 17:48 UTC (Thu) by nix (subscriber, #2304)
In reply to: Fedora and LVM by Cato
Parent article: Fedora and LVM

You see, with LVM that 'moving other partitions around that are not as full' case -- always rather hair-raising -- disappears. All you have to do is possibly shrink one fs and expand another one.

I've ended up leaving most space in a VG free until I need it, which means I hardly ever have to shrink fses at all (a good thing because most fses cannot be shrunk without being unmounted). This makes expanding an fs that's out of space, no matter whether it's immediately followed by another fs or not, a matter of five minutes' work with no unmounting, no loss of service, and a near-zero chance of data loss. You just *cannot* do that without some LVM-like indirection layer (in btrfs and ZFS's case, inside the filesystem itself).

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Fedora and LVM

Posted Nov 1, 2012 21:29 UTC (Thu) by rleigh (subscriber, #14622) [Link]

I did this until very recently. I've used LVM on all my systems since LVM came into being, and did online resizing of LVs as and when required. But after recently acquiring an SSD, the system is on Btrfs, with subvolumes used where I would previously have had LVs. No problems so far, though I'm not yet so trusting that /home and /var are still on ext4 on LVM+mdraid. I might move them over once I have gained more trust in it, though after losing an entire RAID1 Btrfs filesystem after a SATA cable glitch earlier in the year, that won't be for a good while.

For me at least the Btrfs improvements are the immediate snapshotting at the FS level, and that the free space is available to all partitions--I don't have to allocate the space up front to the different subvolumes. It would be great if the distribution installers would automatically use subvolumes appropriately when installing onto Btrfs, though I've not checked recently to see how this improved.

Fedora and LVM

Posted Nov 2, 2012 7:17 UTC (Fri) by Cato (subscriber, #7643) [Link]

I guess it comes down to trusting GParted to get it right for the partition resizing and moving, with it generating all the various commands - I have yet to lose data when using a reasonably recent Gparted and kernel, whereas with LVM there are quite a few commands to get exactly right, and due to write caching/barrier problems on older kernels I have lost data through LVM.