[kwlug-disc] BTRFS Was: Transferring large backup files over the network

[Remi Gauvin]

On 2019-05-23 8:07 p.m., CrankyOldBugger wrote:
> We looked at BTRFS at work a few months ago and decided that it wasn't
> ready for prime time yet.  I wonder if it's improved since then?  We're
> happy with ext4 and LVM.
> 

I've been using it quite successfully in multiple places for a couple
years, and am *very* pleased with the way it handles Snapshots.  Snapper
on a nas share is a godsend.

That being said, I'm comfortable to keep an eye out on the development
mailing list and being aware of potential pitfalls... I don't think it's
'ready' for prime time use by the general public.

<rant>
For example, one of my favorite pet peeve problems that is ignored by
the developers is the complete disfunction of BTRFS raid and files with
COW disabled.  Due to some very heavy performance loss on workloads with
lots of random writes and fsync, many places, including the official
BTRFS wiki, recommend disabling Copy-On-Write for database or VM Image
files.  However, the BTRFS raid implementation is completely dependent
on CoW to maintain synchronization between mirrors.  Any event that
interrupts writes to a mirrored file with CoW disabled will result in
discrepancies between the mirrored copies, and they are never
automatically fixed.. not even if you run a scrub.  The data that gets
read from the file will be different depending on which drive your
system happens to choose to read from that second.
</rant>

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