Hi, Stefan Monnier wrote: > Presumably the "backuper" is the sysadmin, i.e. the same (group of) > person who chose the filesystem, so I'd say yes the "backuper" is > to blame.
I rather mean the whole complex of system maintainer, users, and backup software. But even if there is a qualified entity to be blamed, this does not help with potential backup problems, because the backup cannot wait until the culprit feels responsible and finds a way to fix the shortcommings. > BTW, I can't think of any filesystem that can't do snapshots. E.g. I use > snapshots with ext4: just ask your block layer to do the snapshot rather > than your filesystem (in my case I use LVM snapshots). It took me a while to find out how the block layer can ensure that a snapshot is consistent on the filesystem level. The answer is Linux VFS method super_operations.freeze_fs(). https://www.kernel.org/doc/html/latest/filesystems/vfs.html Without it a snapshot on block level would be similar to a filesystem which was not properly unmounted before power-off. So there might still filesystems in the Linux kernel which do not support LVM snapshots in a safe way. https://manpages.debian.org/bullseye/util-linux/fsfreeze.8.en.html states about filesystems with freeze capability: "List of these filesystems include (2016-12-18) btrfs, ext2/3/4, f2fs, jfs, nilfs2, reiserfs, and xfs." That's quite comprehensive, but by far not the full list of writable Linux fileystems. One would have to dig in the kernel whether others have gained a .freeze_fs method meanwhile. I looked in the torvalds git repo at the super_operations structs of exfat, fat, fuse, and udf. None of them offers the freeze_fs method. Have a nice day :) Thomas
