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Subject: Re: btrfs-cleaner / snapshot performance analysis
To: Hans van Kranenburg <hans.van.kranenburg@mendix.com>,
        "Ellis H. Wilson III" <ellisw@panasas.com>,
        linux-btrfs@vger.kernel.org
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 <96cd9e57-cde4-5bc4-0312-02b54668e59a@mendix.com>
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From: Andrei Borzenkov <arvidjaar@gmail.com>
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Date: Sun, 11 Feb 2018 12:31:42 +0300
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11.02.2018 04:02, Hans van Kranenburg пишет:
...
> 
>> - /dev/sda6 / btrfs
>> rw,relatime,ssd,space_cache,subvolid=259,subvol=/@/.snapshots/1/snapshot
>> 0 0
> 
> Note that changes on atime cause writes to metadata, which means cowing
> metadata blocks and unsharing them from a previous snapshot, only when
> using the filesystem, not even when changing things (!).

With relatime atime is updated only once after file was changed. So your
description is not entirely accurate and things should not be that
dramatic unless files are continuously being changed.