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From: Efraim Flashner <efraim@flashner.co.il>
To: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Cc: "Ludovic Courtès" <ludo@gnu.org>,
	"Pierre Neidhardt" <mail@ambrevar.xyz>,
	40236@debbugs.gnu.org,
	"Jonathan Brielmaier" <jonathan.brielmaier@web.de>
Subject: [bug#40236] [PATCH] doc: Suggest Btrfs with compression instead of ext4 for root partition.
Date: Mon, 1 Jun 2020 09:16:03 +0300	[thread overview]
Message-ID: <20200601061603.GF7397@E5400> (raw)
In-Reply-To: <878sh75scf.fsf@gmail.com>

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> >
> > 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
tests.

> > 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 inline.
> 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   <efraim@flashner.co.il>   אפרים פלשנר
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  reply	other threads:[~2020-06-01  6:17 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26  8:35 [bug#40236] [PATCH] doc: Suggest Btrfs with compression instead of ext4 for root partition Pierre Neidhardt
2020-03-31  1:52 ` Maxim Cournoyer
2020-03-31  7:52   ` Pierre Neidhardt
2020-03-31 14:53   ` Pierre Neidhardt
2020-03-31 23:20     ` Maxim Cournoyer
2020-04-01  7:00       ` Pierre Neidhardt
2020-05-02 13:29         ` Pierre Neidhardt
2020-05-02 13:50           ` Marius Bakke
2020-05-02 13:58             ` Pierre Neidhardt
2020-05-02 19:03               ` Maxim Cournoyer
2020-05-03  7:01                 ` Pierre Neidhardt
2020-05-04 15:22                   ` Maxim Cournoyer
2020-04-01 21:28   ` Ludovic Courtès
2020-04-02  7:15     ` Pierre Neidhardt
2020-04-02  8:04       ` Ludovic Courtès
2020-04-02 10:36         ` Jonathan Brielmaier
2020-04-04  1:28         ` Maxim Cournoyer
2020-04-06 20:20           ` Pierre Neidhardt
2020-04-06 20:42             ` Jonathan Brielmaier
2020-04-07  7:07               ` Pierre Neidhardt
2020-04-08  3:18                 ` Maxim Cournoyer
2020-04-09 20:12                   ` Efraim Flashner
2020-04-10  7:39                     ` Pierre Neidhardt
2020-04-10  8:24                       ` Efraim Flashner
2020-04-10  9:04                         ` Pierre Neidhardt
2020-04-14  2:20                           ` Maxim Cournoyer
2020-04-14  6:53                             ` Pierre Neidhardt
2020-05-31  7:39                               ` Pierre Neidhardt
2020-05-31  7:55                                 ` Efraim Flashner
2020-06-01  4:21                                   ` Maxim Cournoyer
2020-06-01  6:16                                     ` Efraim Flashner [this message]
2020-06-01  7:48                                       ` Pierre Neidhardt
2020-06-01 18:29                                         ` Maxim Cournoyer
2020-05-31 21:07                                 ` Ludovic Courtès
2020-06-01  5:03                                   ` Maxim Cournoyer
2020-06-02 13:37                                   ` Pierre Neidhardt
2020-06-03 20:00                                     ` bug#40236: " Ludovic Courtès
2020-06-04  9:17                                       ` [bug#40236] " Pierre Neidhardt
2020-06-01  4:49                                 ` Maxim Cournoyer
2020-03-31 12:09 ` Jonathan Brielmaier

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