Re: Snapper & apt-btrfs-snapshot on Ubuntu

[Duncan <1i5t5.duncan@cox.net>]

Ahmed Badr posted on Wed, 02 Nov 2016 02:00:55 +0200 as excerpted:

> Btrfs newbie here trying to figure out how to use it properly on Ubuntu
> 16.04 server.
> 
> I have root formated using Btrfs, and installed Snapper [...]

I see Hans answered your direct question so I'll skip that, but one 
additional hint, in case you hadn't seen it yet and your snapshot 
management helpers aren't setup to take care of this automatically 
(possibly because you're using two of them)...

Btrfs tends to have scaling issues if you let the number of snapshots get 
too high.  Try to keep it under 300 snapshots per subvolume (combined 
between all tools) if at all possible, and if your use-case makes it easy 
enough, try to keep it under 100 snapshots per subvolume.  Definitely 
don't let it get into the thousands of snapshots per subvolume, or 
commands such as btrfs balance and btrfs check will take MUCH longer and 
use MANY TIMES more memory.

With automated snapshot management such as snapper, just make sure it's 
thinning down the snapshots at a reasonable rate as well, and ultimately 
deleting the oldest ones.  With proper thinning, it's easily possible to 
keep to around 250-ish snapshots, even starting at ever half hour or so.  
With that, proper thinning probably means thinning down to perhaps every 
hour to every three hours after 24 hours, then to two snapshots a day 
after a couple more days and one a day after a week.  Continue thinning 
after that, until after say a quarter (13 weeks) you're only keeping one 
a week, and after six months you're only keeping quarterly snapshots -- 
if you're not deleting all snapshots at six months because you switch to 
alternative media backups before that.

The thing for you is that since you're using two different automated 
snapshot tools, you need to make sure the combined total still stays 
below that 300, and below 100 if your use-case can handle it, as it'll 
definitely mean more efficient processing if you need to run a balance or 
check.

Second tip, btrfs quotas can make the scaling issues much worse.  If your 
use-case doesn't require them, simply turn them off (or never activate 
them in the first place) and avoid the management complexity they bring.  
A number of people have reported problems that simply disappeared when 
they turned off btrfs quotas, so being proactive and turning them off if 
you don't need them, to avoid having the issues in the first place, 
certainly can't hurt.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman