4 ms·
ZFS, Btrfs do this with COW. NTFS (volume snapshot service) and ReFS makes it COW. LVM2 offers a new thinp COW based snapshot that could make this work for any
by cmurf 12y ago
ZFS, Btrfs do this with COW. NTFS (volume snapshot service) and ReFS makes it COW. LVM2 offers a new thinp COW based snapshot that could make this work for any filesystem.
Edit: And Apple's CoreStorage also has some kind of COW capability at least when used for "fusion" drives. And then Time Machine and OSTree are effectively COW as well. The trick here is how to make what's written, read-only and thus write once. Btrfs at least has the concept of read-only seed devices, which can be put together in sequence, but might need some work to make it fit better with this use case.
- cmurf 12y agoIf delaying the "write once" aspect of a volume (or tree) is OK, several of the above options offer read-only snapshots. Btrfs ro snapshots aren't writable even by root. They can be deleted or a rw snapshot can be made from them.
- enneff 12y agoIIUC both ZFS and btrfs require that you be root to work with file system snapshots.
- cmurf 12y agoOn Btrfs an unprivileged user can create subvolumes/snapshots. There's a mount option that lets them remove subvolumes they own.
- enneff 12y agoI didn't know that. Very cool!
- 4ad 12y agoSolaris has a fine-grained privilege model where you can delegate any aspect of any dataset to any user. However, FreeBSD and Linux don't have this, so on those systems you have to be root to do snapshots.
- enneff 12y agoAh, I see. I've only used ZFS on FreeBSD so I guess I'm missing out. Thanks.