On 08.01.2018 19:34 Austin S. Hemmelgarn wrote: > On 2018-01-08 13:17, Graham Cobb wrote: >> On 08/01/18 16:34, Austin S. Hemmelgarn wrote: >>> Ideally, I think it should be as generic as reasonably possible, >>> possibly something along the lines of: >>> >>> A: While not strictly necessary, running regular filtered balances (for >>> example `btrfs balance start -dusage=50 -dlimit=2 -musage=50 >>> -mlimit=4`, >>> see `man btrfs-balance` for more info on what the options mean) can >>> help >>> keep a volume healthy by mitigating the things that typically cause >>> ENOSPC errors. Full balances by contrast are long and expensive >>> operations, and should be done only as a last resort. >> >> That recommendation is similar to what I do and it works well for my use >> case. I would recommend it to anyone with my usage, but cannot say how >> well it would work for other uses. In my case, I run balances like that >> once a week: some weeks nothing happens, other weeks 5 or 10 blocks may >> get moved. > > In my own usage I've got a pretty varied mix of other stuff going on. > All my systems are Gentoo, so system updates mean that I'm building > software regularly (though on most of the systems that happens on > tmpfs in RAM), I run a home server with a dozen low use QEMU VM's and > a bunch of transient test VM's, all of which I'm currently storing > disk images for raw on top of BTRFS (which is actually handling all of > it pretty well, though that may be thanks to all the VM's using > PV-SCSI for their disks), I run a BOINC client system that sees pretty > heavy filesystem usage, and have a lot of personal files that get > synced regularly across systems, and all of this is on raid1 with > essentially no snapshots. For me the balance command I mentioned > above run daily seems to help, even if the balance doesn't move much > most of the time on most filesystems, and the actual balance > operations take at most a few seconds most of the time (I've got > reasonably nice SSD's in everything).
There have been reports of (rare) corruption caused by balance (won't be detected by a scrub) here on the mailing list. So I would stay a away from btrfs balance unless it is absolutely needed (ENOSPC), and while it is run I would try not to do anything else wrt. to writes simultaneously. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
