[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[bug#40236] [PATCH] doc: Suggest Btrfs with compression instead of ext4
[bug#40236] [PATCH] doc: Suggest Btrfs with compression instead of ext4 for root partition.
Mon, 1 Jun 2020 09:16:03 +0300
> > Two more things:
> > /var/guix/db should probably have CoW disabled, as should /tmp
> I haven't bothered and my system seems to be doing OK. When I asked in
> #btrfs, people told me to keep CoW unless I was really sure it was a
> problem (i.e., run benchmarks), as it implies loosing the checksum
> validation and compression. The command 'man 5 btrfs' also states that
> "Updates in-place improve performance for workloads that do frequent
> overwrites, at the cost of potential partial writes, in case the write
> is interrupted (system crash, device failure).", which doesn't sound
> safe to do for something as important as /var/guix/db.
Fair enough. I had heard that the CoW stuff wasn't great for databases.
I thought Leo ran into some issues with CoW on /tmp with the syncthing
> > would the deduplication of btrfs be "better" than the deduplication from
> > the daemon?
> On my system (with zstd compression), compsize -x /gnu/store suggests
> a resounding yes:
> --8<---------------cut here---------------start------------->8---
> sudo compsize -x /gnu/store
> Processed 3479664 files, 954748 regular extents (3002677 refs), 1451082
> Type Perc Disk Usage Uncompressed Referenced
> TOTAL 57% 51G 88G 217G
> none 100% 32G 32G 81G
> zstd 33% 18G 56G 135G
> --8<---------------cut here---------------end--------------->8---
> The delta between the Uncompressed and Referenced column is attributed
> to the deduplication done by Btrfs, and provides massive space savings
> in my case (this is just for /gnu/store).
> I'd need 217 GiB over a traditional fs such as EXT4 to hold my current
> store, while an uncompressed Btrfs partition would use only 88 GiB.
> With zstd compression, it's down to 51 GiB, or less that a quarter of
> what would have been required using EXT4.
I always understood that as with compression you're using 51G instead of
88G, and because of deduplication from the daemon it would only be 88G
instead of 217G. I took the numbers from 'none' to mean that the daemon
itself already did a lot of deduplication.
Efraim Flashner <email@example.com> אפרים פלשנר
GPG key = A28B F40C 3E55 1372 662D 14F7 41AA E7DC CA3D 8351
Confidentiality cannot be guaranteed on emails sent or received unencrypted
Description: PGP signature