Comment on Why and when should I use LVM?
poVoq@slrpnk.net 10 months ago
Slightly off tangent, but if you are thinking you might need LVM features (other than disk encryption) then it is worth looking into filesystem’s that have most of the functionality built in, like btrfs or OpenZFS.
rentar42@kbin.social 10 months ago
I'm torn a bit, because architecturally/conceptually the split that LVM does is the correct way: have a generic layer that can bundle multiple block devices to look like one and let any old filesystem work on top of that. It's neat, it's clean, it's unix-y.
But then I see what ZFS (and btrfs, but I don't use that personally) do while "breaking" that neat separation and it's truly impressive. Sometimes tight integration between layers has serious advantages too and neat abstraction layers don't work quite as well.
Sowhatever@discuss.tchncs.de 10 months ago
Care to elaborate about these ZFS features?
rentar42@kbin.social 10 months ago
ZFS combines the features of something like LVM (i.e. spanning multiple devices, caching, redundancy, ...) with the functions of a traditional filesystem (think ext4 or similar).
Due to that combination it can tightly integrate the two systems and not treat the "block level" as an opaque layer. For example each data block in ZFS is stored with a checksum, so data corruption can be detected. If a block is stored on multiple devices (due to a mirroring setup or raid-z) then the filesystem layer will read multiple blocks when it detects such a data corruption and re-store the "correct" version to repair the damage.
First off most filesystems (unfortunately and almost surprisingly) don't do that kind of checksum for their data: when the HDD returns rubbish they tend to not detect the corruption (unless the corruption is in their metadata in which case they often fail badly via a crash).
Second: if the duplication was handled via something like LVM it couldn't automatically repair errors in a mirror setup because LVM would have no idea which of the blocks is uncorrupted (if any).
ZFS has many other useful (and some arcane) features, but that's the most important one related to its block-layer "LVM replacement".
Sowhatever@discuss.tchncs.de 10 months ago
Very interesting, thanks for the message. I might use it in my next Nas, but my workstation is staying on regular lvm, too much hassle to change probably…