Btrfs best practices
Hi! I own a Dell Inspiron 5570 laptop with 1 TB SATA HDD, a new 250 GB
NVMe SSD¹ and 16 GiB RAM. I seek reliability, durability, performance
and power efficiency.
I do weekly duplicity backups to external 1.5 TB USB3 HDD. I'll start
also daily rsyncing some of the SSD data to the SATA HDD.
The SSD will have 50 GB extra over provisioning and a 200 GB partition,
besides the special UEFI partition. The SATA HDD will start with 16 GiB
swap partition then a big partition. I'll put system and /home on the
SSD but all XDG user dirs² on the HDD, and tmpfs on /tmp. All three
drives will have Btrfs with space_cache=v2, noatime, zstd compression
and reasonable free breathing space.
I use Gnome and:
- GNU Emacs
- notmuch and offlineimap (I may switch to mbsync)
- GNU IceCat, Mozilla Firefox and ungoogled-chromium
- Gajim and GNU Jami
- Gnome Boxes or Virtual Machine Manager running a VM with 2 GiB RAM and
one .qcow2 disk image currently weighting 24 GB.
- mpv
- Nextcloud (always running but rarely syncing changes)
I use Debian stable with only official repositories, including
bullseye-backports. I manually installed GNU Guix package manager and
have 163 packages on main Guix profile.
* Doubts
** Backported kernel
Should I use a backported kernel as Btrfs [wiki][] recommends? I worry
that bullseye-backports comes from Debian testing with poor security.
[wiki]: https://btrfs.wiki.kernel.org/index.php/Getting_started#Before_you_start
** Strong compression during install
For lifetime and space saving, I intend to install Debian to the SSD
with compress-force=zstd:12, but then adopt compress-force=zstd. Thus
the installation will be slow---I'll do something else while the
installer works---but the installed system will be efficient, right?
** HDD Compression
Both HDD have a lot of already-compressed data: videos, audio, photos
and compressed archives and disk images; compress-force would force
Btrfs to recompress it all, only to discard the recompressed data and
store the original. Therefore compress=zstd:4 would be better, right?
** Fragmentation
Is fragmentation a concern? Is the [Gotchas][] article accurate?
[Gotchas]: https://btrfs.wiki.kernel.org/index.php/Gotchas#Fragmentation
** Subvolumes
What about
https://fedoraproject.org/wiki/Changes/BtrfsByDefault#Additional_subvolumes ?
** Swappiness
Most performance-critical data will be on the SSD, so there will be much
less need for RAM caches; therefore I should decrease swappiness
(especially if I put swap on the SSD), right? By how much?
* Footnotes
¹ A 250 GB WD Blue SN550 rated for 150 TBW.
² See the xdg-user-dir manpage.
Kindest regards,
Jorge
--
- Many people hate injustice but few check the facts; this causes more
injustice. Ask me about <https://stallmansupport.org>
- I am Brazilian. I hope my English is correct and I welcome feedback.
- https://www.defectivebydesign.org
- https://www.gnu.org
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