On 13 Jan 2018, at 17:09, Chris Murphy wrote:
On Fri, Jan 12, 2018 at 11:24 AM, Austin S. Hemmelgarn
<ahferro...@gmail.com> wrote:
To that end, I propose the following text for the FAQ:
Q: Do I need to run a balance regularly?
A: While not strictly necessary for normal operations, running a
filtered
balance regularly can help prevent your filesystem from ending up
with
ENOSPC issues. The following command run daily on each BTRFS volume
should
be more than sufficient for most users:
`btrfs balance start -dusage=25 -dlimit=2..10 -musage=25
-mlimit=2..10`
Daily? Seems excessive.
I've got multiple Btrfs file systems that I haven't balanced, full or
partial, in a year. And I have no problems. One is a laptop which
accumulates snapshots until roughly 25% free space remains and then
most of the snapshots are deleted, except the most recent few, all at
one time. I'm not experiencing any problems so far. The other is a NAS
and it's multiple copies, with maybe 100-200 snapshots. One backup
volume is 99% full, there's no more unallocated free space, I delete
snapshots only to make room for btrfs send receive to keep pushing the
most recent snapshot from the main volume to the backup. Again no
problems.
I really think suggestions this broad are just going to paper over
bugs or design flaws, we won't see as many bug reports and then real
problems won't get fixed.
This is just an answer to a FAQ. This is not Austin or anyone else
trying to telling you or anyone else that you should do this. It should
be clear that there is an implied caveat along the lines of: "There are
other ways to manage allocation besides regular balancing. This
recommendation is a For-Dummies-kinda default that should work well
enough if you don't have another strategy better adapted to your
situation." If this implication is not obvious enough then we can add
something explicit.
I also thing the time based method is too subjective. What about the
layout means a balance is needed? And if it's really a suggestion, why
isn't there a chron or systemd unit that just does this for the user,
in btrfs-progs, working and enabled by default?
As a newcomer to BTRFS, I was astonished to learn that it demands each
user figure out some workaround for what is, in my judgement, a required
but missing feature, i.e. a defect, a bug. At present the docs are
pretty confusing for someone trying to deal with it on their own.
Unless some better fix is in the works, this _should_ be a systemd unit
or something. Until then, please put it in FAQ.
I really do not like
all this hand holding of Btrfs, it's not going to make it better.
Maybe it won't but, absent better proposals, and given the nature of the
problem, this kind of hand-holding is only fair to the user.
Tom
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