Krissy Silvermoon Aug 22, 2023

#BTRFS advice.

This is a Filesystem that can do really awesome things... but it's worth noting that some of those things generate LOTS of fragmentation.

On SSDs this won't matter too much.
On Spinnybois though? Definitely be mindful of what you're doing or you'll feel every bit of that.

I generally run with 'autodefrag' and on HDDs with 'nodatacow' in my mount options. CopyOnWrite generates fragmentation over the course of normal use.

That does NOT mean that CopyOnWrite never happens. It means it doesn't happen when it doesn't *have* to. If you dedupe files with duperemove, create snapshots or make reflink copies, it STILL happens.

Moral of the story, please do not duperemove your databases on a spinnyboi. I had an app go from taking a minute or two to open to just 5 seconds just by defragging the databases.

Show threadinterru
@christiansilvermooon only use "nodatacow" if you actually have a performance problem and need it. nodatacow disables checksums and in context of raid increases the risk of data loss substantially because of non atomic writes.
Aug 24, 2023 at 1:29pmWeb
Show threadKrissy Silvermoon Aug 24, 2023

@interru In the case of of my singular mechanical disk, I'm not relying on the checksum for anything currently

I don't run with 'nodatacow' on SSDs, only HDDs.

Never done a RAID configuration, but if I ever do, thanks for the heads up on that!

In all honesty since one of my disk in question is often read from far more than written to, aside from a few database files I *could* probably disable CoW on just the databases...