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From: Jan Ziak <0xe2.0x9a.0x9b@gmail.com>
To: Phillip Susi <phill@thesusis.net>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Btrfs autodefrag wrote 5TB in one day to a 0.5TB SSD without a measurable benefit
Date: Wed, 9 Mar 2022 22:35:47 +0100	[thread overview]
Message-ID: <CAODFU0oM02WDpOPXp1of177aEJ9=ux2QFrHZF=khhzAg+3N1dA@mail.gmail.com> (raw)
In-Reply-To: <87tuc7gdzp.fsf@vps.thesusis.net>

On Wed, Mar 9, 2022 at 7:47 PM Phillip Susi <phill@thesusis.net> wrote:
> Jan Ziak <0xe2.0x9a.0x9b@gmail.com> writes:
>
> > I noticed this inaccurate wording in my email as well, but that was
> > (unfortunately) after I already sent the email. I was hoping that
> > after examining the compsize logs present in the email, readers would
> > understand what the term "file size" means in this particular case.
>
> I don't understand.  You stated that the size decreased by 7 GB, and the
> size figures that followed appeared to bear that out.

The actual disk usage of a file in a copy-on-write filesystem can be
much larger than sb.st_size obtained via fstat(fd, &sb) if, for
example, a program performs many (millions) single-byte file changes
using write(fd, buf, 1) to distinct/random offsets in the file.

Before running "btrfs fi de file.sqlite": the disk usage of the file
was 47GB, 1834778 extents

After running "btrfs fi de file.sqlite; sync": the disk usage of the
file was 40GB, 13074 extents

Sincerely
Jan

  reply	other threads:[~2022-03-09 21:36 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-06 15:59 Btrfs autodefrag wrote 5TB in one day to a 0.5TB SSD without a measurable benefit Jan Ziak
2022-03-07  0:48 ` Qu Wenruo
2022-03-07  2:23   ` Jan Ziak
2022-03-07  2:39     ` Qu Wenruo
2022-03-07  7:31       ` Qu Wenruo
2022-03-10  1:10         ` Jan Ziak
2022-03-10  1:26           ` Qu Wenruo
2022-03-10  4:33             ` Jan Ziak
2022-03-10  6:42               ` Qu Wenruo
2022-03-10 21:31                 ` Jan Ziak
2022-03-10 23:27                   ` Qu Wenruo
2022-03-11  2:42                     ` Jan Ziak
2022-03-11  2:59                       ` Qu Wenruo
2022-03-11  5:04                         ` Jan Ziak
2022-03-11 16:31                           ` Jan Ziak
2022-03-11 20:02                             ` Jan Ziak
2022-03-11 23:04                             ` Qu Wenruo
2022-03-11 23:28                               ` Jan Ziak
2022-03-11 23:39                                 ` Qu Wenruo
2022-03-12  0:01                                   ` Jan Ziak
2022-03-12  0:15                                     ` Qu Wenruo
2022-03-12  3:16                                     ` Zygo Blaxell
2022-03-12  2:43                                 ` Zygo Blaxell
2022-03-12  3:24                                   ` Qu Wenruo
2022-03-12  3:48                                     ` Zygo Blaxell
2022-03-14 20:09                         ` Phillip Susi
2022-03-14 22:59                           ` Zygo Blaxell
2022-03-15 18:28                             ` Phillip Susi
2022-03-15 19:28                               ` Jan Ziak
2022-03-15 21:06                               ` Zygo Blaxell
2022-03-15 22:20                                 ` Jan Ziak
2022-03-16 17:02                                   ` Zygo Blaxell
2022-03-16 17:48                                     ` Jan Ziak
2022-03-17  2:11                                       ` Zygo Blaxell
2022-03-16 18:46                                 ` Phillip Susi
2022-03-16 19:59                                   ` Zygo Blaxell
2022-03-20 17:50                             ` Forza
2022-03-20 21:15                               ` Zygo Blaxell
2022-03-08 21:57       ` Jan Ziak
2022-03-08 23:40         ` Qu Wenruo
2022-03-09 22:22           ` Jan Ziak
2022-03-09 22:44             ` Qu Wenruo
2022-03-09 22:55               ` Jan Ziak
2022-03-09 23:00                 ` Jan Ziak
2022-03-09  4:48         ` Zygo Blaxell
2022-03-07 14:30 ` Phillip Susi
2022-03-08 21:43   ` Jan Ziak
2022-03-09 18:46     ` Phillip Susi
2022-03-09 21:35       ` Jan Ziak [this message]
2022-03-14 20:02         ` Phillip Susi
2022-03-14 21:53           ` Jan Ziak
2022-03-14 22:24             ` Remi Gauvin
2022-03-14 22:51               ` Zygo Blaxell
2022-03-14 23:07                 ` Remi Gauvin
2022-03-14 23:39                   ` Zygo Blaxell
2022-03-15 14:14                     ` Remi Gauvin
2022-03-15 18:51                       ` Zygo Blaxell
2022-03-15 19:22                         ` Remi Gauvin
2022-03-15 21:08                           ` Zygo Blaxell
2022-03-15 18:15             ` Phillip Susi
2022-03-16 16:52           ` Andrei Borzenkov
2022-03-16 18:28             ` Jan Ziak
2022-03-16 18:31             ` Phillip Susi
2022-03-16 18:43               ` Andrei Borzenkov
2022-03-16 18:46               ` Jan Ziak
2022-03-16 19:04               ` Zygo Blaxell
2022-03-17 20:34                 ` Phillip Susi
2022-03-17 22:06                   ` Zygo Blaxell
2022-03-16 12:47 ` Kai Krakow
2022-03-16 18:18   ` Jan Ziak
2022-06-17  0:20 Jan Ziak

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