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From: Henk Slager <eye1tm@gmail.com>
Date: Tue, 5 Sep 2017 14:49:51 +0200
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Subject: Re: Is autodefrag recommended?
To: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
Cc: linux-btrfs <linux-btrfs@vger.kernel.org>
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On Tue, Sep 5, 2017 at 1:45 PM, Austin S. Hemmelgarn
<ahferroin7@gmail.com> wrote:

>>   - You end up duplicating more data than is strictly necessary. This
>>     is, IIRC, something like 128 KiB for a write.
>
> FWIW< I'm pretty sure you can mitigate this first issue by running a regular
> defrag on a semi-regular basis (monthly is what I would probably suggest).

No, both autodefrag and regular defrag duplicate data, so if you keep
snapshots around for weeks or months, it can eat up a significant
amount of space.