hello -
thanks for the feedback... some comments inline. i must stress that
while i am a multi-year user of btrfs i do not read the linux-btrfs
mailing list and my opinions should be given appropriate weight.
On Sat, 2023-01-14 at 21:47 -0500, Nicholas D Steeves wrote:
>
[...]
> Oh yeah! I had forgotten about this minor issue. The reason I
> hadn't
> harmonised the files, doing this implicitly says that I (and Debian)
> might recommend weekly balanced, or recommend monthly balances.
>
> From what I've been able to gather, metadata balances have been
> considered to be actively harmful for some time; This is mostly at
> the
> level of tribal knowledge on the linux-btrfs mailing list. It's also
> the case that empty block groups are now automatically reclaimed by
> the
> kernel, so a periodic balance only seems to be useful in
> space-constrained situations where a lot of [meta]data churn occurs.
regarding balance recommendations, my initial thought would be to make
the language in the README.Debian stronger. i had read that "Some
advocate not running it at all" but to me that implies "may be
unnecessary" rather than "may be actively harmful." on the basis of
the latter i am certainly considering setting the balance.timer back to
disabled. alternatively/additionally are there default options that
might make it safe(r)? e.g., Marc MERLIN's `btrfs-scrub`[1] (which i
used previously) suggested that "a null [metadata] rebalance should
help corner cases."
from my pov i'd still like to see the values harmonized. i originally
noticed the inconsistency because what i believed was the default
setting was creating a seemingly unnecessary systemd override file.
this became a nagging question to resolve :) if the (informed) user
has chosen to enable the btrfs-balance.timer then i would say harmonize
the value at "monthly" (1/4 the opportunity for issues).
> Thus, if I do anything, I'm inclined to set the period for balance to
> "none" everywhere.
given that one already needs to manually enable the service via
`systemctl enable btrfs-balance.timer` i don't think it's necessary to
set the default value to "none." this would result in the (imho)
counter-intuitive behavior of enabling something only to have it do
nothing. although an add'l comment re: the potential for harm in
`/etc/default/btrfs` that one would hopefully see when changing the
value from "none" to e.g., "monthly" may be the best way to ensure that
they are an informed user. so i could go either way on that.
> Also, what do you think about enabling the systemd patch watcher, so
> that the timers are updated automatically when
> /etc/default/btrfsmaintenance is modified?
as a sysadmin the steps of modifying a file and then running a command
for it to take effect is a normal part of my workflow. so i'm fine
leaving it disabled by default. other users might feel differently.
thank you...
andy
1. https://marc.merlins.org/linux/scripts/btrfs-scrub
--
andy <and...@diatribes.org>
diatribes
