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Date: Sun, 11 Sep 2016 19:46:32 +0000
From: Hugo Mills <hugo@carfax.org.uk>
To: Martin Steigerwald <martin@lichtvoll.de>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Small fs
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On Sun, Sep 11, 2016 at 09:13:28PM +0200, Martin Steigerwald wrote:
> Am Sonntag, 11. September 2016, 16:44:23 CEST schrieb Duncan:
> > * Metadata, and thus mixed-bg, defaults to DUP mode on a single-device=
=20
> > filesystem (except on ssd where I actually still use it myself, and=20
> > recommend it except for ssds that do firmware dedupe).  In mixed-mode=
=20
> > this means two copies of data as well, which halves the usable space.
> >=20
> > IOW, when using mixed-mode, which is recommended under a gig, and dup=
=20
> > replication which is then the single-device default, effective usable=
=20
> > space is **HALVED**, so 256 MiB btrfs size becomes 128 MiB usable. (!!)
>=20
> I don=B4t get this part. That is just *metadata* being duplicated, not th=
e=20
> actual *data* inside the files. Or am I missing something here?

   In mixed mode, there's no distinction: Data and metadata both use
the same chunks. If those chunks are DUP, then both data and metadata
are duplicated, and you get half the space available.

   Hugo.

--=20
Hugo Mills             | Questions are a burden, and answers a prison for
hugo@... carfax.org.uk | oneself
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                          The Priso=
ner

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