From: Roman Mamedov <rm@romanrm.net>
To: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Cc: "Christian Völker" <cvoelker@knebb.de>,
"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: Removal of Device and Free Space
Date: Sat, 15 May 2021 12:48:03 +0500 [thread overview]
Message-ID: <20210515124803.41f88f70@natsu> (raw)
In-Reply-To: <20210515013903.GE32440@hungrycats.org>
On Fri, 14 May 2021 21:39:04 -0400
Zygo Blaxell <ce3g8jdj@umail.furryterror.org> wrote:
> > What is occupying so much disk space as the data only has 1.7TB which
> > should fit in 1.8TB (two) devices? (no snapshot, nothing special configured
> > on btrfs). Looks like there are ~400GB allocated which are not from data.
>
> Chunks are deallocated only when completely empty. If you recently
> deleted a large number of files, then you'll have chunks with low data
> density and high free space fragmentation. Normally this does not matter,
> as the free spaces in chunks would be filled in by new data allocations,
> and those allocations would split writes into smaller extents that exactly
> fit the free spaces. Relocation can't do this--it can only occupy free
> spaces that are equal or larger, and will make free space fragmentation
> even worse.
Oh yeah, if you were just talking about discrepancy between "allocated" vs
"used", then it is what Zygo said, and my other reply regrading extent booking
doesn't apply here. That other issue is relevant only if you observe a
difference between "du [all files]" and "df [filesystem]".
--
With respect,
Roman
next prev parent reply other threads:[~2021-05-15 7:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 8:54 Removal of Device and Free Space Christian Völker
2021-05-14 16:44 ` Andrei Borzenkov
2021-05-14 17:06 ` Roman Mamedov
2021-05-14 19:54 ` Christian Völker
2021-05-14 21:55 ` Remi Gauvin
2021-05-15 1:39 ` Zygo Blaxell
2021-05-15 7:48 ` Roman Mamedov [this message]
2021-05-16 18:41 ` Christian Völker
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