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List:       fedora-devel-list
Subject:    Re: Fedora 33 System-Wide Change proposal: Make btrfs the default file system for desktop variants
From:       Dominique Martinet <asmadeus () codewreck ! org>
Date:       2020-07-11 12:20:57
Message-ID: 20200711122057.GA19340 () nautica
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Artem Tim wrote on Sat, Jul 11, 2020:
> BTRFS WA is ~8 times higher than ext4. Average profit from compression
> about 50% max. Not that hard arithmetic.

It's not that simple.
The pattern used in that paper is far from a standard workload (random
writes within a file with cow is just about as bad as things can get
wrt. write amplification) ; so things like the sqlite db firefox uses in
your home will be worse as far as that goes with btrfs even if
compressed yes certainly.

But if you're talking open w/ truncate (or new file), write in a single
stride, close and never write again (like what happens when you upgrade
packages, compile something, download something etc etc) then the
difference won't be that big.

As Chris said multiple times, it's hard to find the right way to measure
impacts, and I don't have good solutions either, but this definitely
isn't the kind of usage I make of my filesystem.
I'd be tempted to believe the feedback from facebook on that one, even
if adding snapshots into the mix it's not 100% clear if compression has
much impact by itself either...



BTW, given the size gains ws. time difference for compression I would
advocate for default zstd compression instead of :1 -- I'd think another
12% compression improvement[1] for almost no time difference isn't to be
sneezed at?

[1] https://www.spinics.net/lists/fedora-devel/msg274978.html
-- 
Dominique
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