On Fri, Jul 28, 2017 at 06:20:14PM +0000, William Muriithi wrote: > Hi Roman, > > > autodefrag > > This sure sounded like a good thing to enable? on paper? right?... > > The moment you see anything remotely weird about btrfs, this is the first > thing you have to disable and retest without. Oh wait, the first would be > qgroups, this one is second. > > What's the problem with autodefrag? I am also using it, so you caught my > attention when you implied that it shouldn't be used. According to docs, it > seem like one of the very mature feature of the filesystem. See below for > the doc I am referring to > > https://btrfs.wiki.kernel.org/index.php/Status > > I am using it as I assumed it could prevent the filesystem being too > fragmented long term, but never thought there was price to pay for using it
It introduces additional I/O on writes, as it modifies a small area surrounding any write or cluster of writes. I'm not aware of it causing massive slowdowns, in the way the qgroups does in some situations. If your system is already marginal in terms of being able to support the I/O required, then turning on autodefrag will make things worse (but you may be heading for _much_ worse performance in the future as the FS becomes more fragmented -- depending on your write patterns and use case). Hugo. -- Hugo Mills | Great oxymorons of the world, no. 6: hugo@... carfax.org.uk | Mature Student http://carfax.org.uk/ | PGP: E2AB1DE4 |
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