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Date:   Thu, 23 Apr 2020 14:05:59 +0200
From:   Marek Behun <marek.behun@nic.cz>
To:     Filipe Manana <fdmanana@gmail.com>
Cc:     Chris Murphy <lists@colorremedies.com>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: when does btrfs create sparse extents?
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On Thu, 23 Apr 2020 12:51:32 +0100
Filipe Manana <fdmanana@gmail.com> wrote:

> There's nothing in btrfs that converts a sequence of zeroes
> automatically to a hole.
> 
> It always has to be done by user space, either by writes that leave
> holes intentionally (e.g. create file, write 64K to offset 0, write 4K
> to offset 128, leaves a hole from range 64K to 128K) or by hole
> punching through fallocate().

Thanks for this information. If you ever come to Prague, let me know,
we can have a beer :D