Crontab
a year ago
This reminds me of APFS's Clone files:
allanjude
a year ago
It is, except it lets you do it as a sub-file level. You can clone a (block aligned) byte range of a file using the copy_file_range() syscall
Accelerating ZFS with Copy Offloading: BRT
33 pointsposted a year ago
by tinyhands12 Comments
awiesenhofer
a year ago
Oh wow, this will be a gamechanger on rsnapshot, restic, etc. Basically every backup workload - can't wait!
cb5r
a year ago
Very interesting feature! Can anyone think of a real world use case for this?
anotherhue
a year ago
Instantiating VMs from snapshots I assume.
allanjude
a year ago
There are a few different use cases, but cloning a VM image file is definitely a popular one.
Also, `mv` between different filesystems in the same ZFS pool. Traditionally when crossing filesystems doesn't allow just using `rename()`, `mv` resorted to effectively `cp` then `rm`, so at least temporarily required 2x the space, and that space might not be freed for a long time if you have snapshots.
With BRT, the copy to the 2nd filesystem doesn't need to write anything more than a bit of metadata, and then when you remove the source copy, it actually removes the BRT entry, so there is no long-term overhead.
One of the original developer's use cases was restoring a file from a snapshot, without having to copy it and have it take up additional space.
So you make a file (foo) 2 days ago. You change it each day. Today, the change you made was bad, and you want to restore the version from yesterday.
before BRT: you copied the file from the snapshot back to the live filesystem, and it took up all new space.
after BRT: we reference the existing blocks in the snapshot, so the copy to the live filesystem takes no additional space on disk. A small BRT entry is maintained in memory (and on disk).
If you remove the snapshot, the BRT entry is removed, and the file remains intact. No long term overhead.
JackSlateur
a year ago
tldr: zfs implemented reflinking (in their own way, not through VFS, sadly)
allanjude
a year ago
There are advantages to doing the cloning at the block level, rather than the VFS layer. The feature was originally written for FreeBSD using the copy_file_range() syscall, then extended to work with the existing interfaces in Linux from btrfs.
burnte
a year ago
New account, no comments, two submissions to klarasystems.com. Seems like a marketing account.
PaulCarrack
a year ago
Perhaps, but still an informative article. Historically, Rob Norris and Klara Systems have contribute a good deal of features and needed bug fixes into OpenZFS.