[pdimitar]

> The dm layer gives you cow/snapshots for any filesystem you want already and has for more than a decade. Some implementations actually use it for clever trickery like updates, even.

O_o

Apparently I've been living under a rock, can you please show us a link about this? I was just recently (casually) looking into bolting ZFS/BTRFS-like partial snapshot features to simulate my own atomic distro where I am able to freely roll back if an update goes bad. Think Linux's Timeshift with something little extra.

[tux3]

There are downsides to adding features in layers, as opposed to integrating them with the FS, but dm can do quite a lot:

https://docs.kernel.org/admin-guide/device-mapper/snapshot.h...

[tptacek]

DM has targets that facilitate block-level snapshots, lazy cloning of filesystems, compression, &c. Most people interact with those features through LVM2. COW snapshots are basically the marquee feature of LVM2.