Re: Is anyone using btrfs send/receive for backups instead of rsync?

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On Sat, Dec 28, 2013 at 2:52 PM, Emil Karlson <jekarlson@xxxxxxxxx> wrote:
>> Emil, your bug report mentions the subvolume journal is different, and
>> not anything about silent content differences on file data (images,
>> databases, etc.) as you mention above.  How are they related?
>
> systemd-journald is a logging daemon in the userspace that has nothing
> to do with filesystem journal.

Ah yes, of course.  I haven't used systemd very much, and was rather
focused on filesystem terminology. (It didn't help that I ignored the
path in your shasum output; but, yes I saw it.)  Sorry!

Though, I'm left wondering what the impact is to systemd.

Is the journal on the received side useless?  I'll read details ; but
I'm guessing the "difference" is that all the used extents were
copied, but that unused but pre-allocated extents were not ; so that
the journal is still has the data systemd has written, but is missing
the empty/unused extents?  However, in that case, I'm unclear about
what sha1sum is reading vs. what systemd is reading - I suppose
systemd must know to ignore extents it has not [yet] written.

>
>> Also, how is the journal different on the receive-side?  Is it "just"
>> a size/allocation issue, as David commented on the bug report; or is
>> the content actually different? For example, can it still be used to
>> recover the filesystem post-crash?  What does "fixed in V2" mean:
>> BTRFSv2 ?
>
> Send stream format specification V2.

Ok, thanks.

(I assume the "Send stream v2 draft", here:
https://btrfs.wiki.kernel.org/index.php/Design_notes_on_Send/Receive )

Regards,
Richard
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