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Re: Questions about a script for regular backups

From: Pierre Fourès <pierre.foures_at_gmail.com>
Date: Fri, 23 Aug 2019 10:15:47 +0200


Le jeu. 22 août 2019 à 16:47, Mark Phippard <markphip_at_gmail.com> a écrit :
>> Cannot they become obsolete when a new version of SVN comes
>> out?
> No. It is a valid copy of the repository.
>> Are they portable across operating systems and
>> filesystems? (I fear not)
> Yes, they are absolutely portable across OS and FS. As is the repos itself.

This prove to work in practice, but is it guaranteed that the fsfs
repos format remain compatible between 1.X subsequent subversion
releases ?

It appears the fsfs repos format sometime change between 1.X
subversion releases. For example, Subversion 1.9 introduced fsfs
format version 7. The release notes [1] mention and recommend to do a
full dump / load cycle to be able to take benefits of this new format
improvements. Nonetheless, the notes also say that "older formats
remain supported". But this seems to be a beneficial side effect, not
a guarantee. It not seem enforced that backward compatibility will be
ensured for all 1.X subsequent subversion releases. To my
understanding, what's guaranteed to remain stable and compatible
between 1.X releases is the protocol between client and server, not
the underlying storing system. This is the reason I went to use
hot-copies for backups *and* dumps for migrations / reinstall. First
off all, it ensures that I will use the latest repos format available
for the particular instance of subversion I would run, and not miss to
upgrade it in order to take all benefits introduced by the targeted
subversion instance. Then, it ensures that in the case of un expected
situation where I would need to downgrade the subversion server
version, I wouldn't face the case of an upgraded fsfs repos format
unable to be read / handled by the said instance.

To my understanding, albeit very slow to load, dumps are absolutely
portable, meaning backward and forward compatible between subversion
server version. You mention the repos are absolutely portable across
OS and FS. Do you also mean between different subversion server
versions ? For instance, how would have it been handled if, by the
time Debian Jessie was out as the Stable Debian, and providing
subversion 1.8, I would have run subversion 1.9 on Ubuntu Xenial (and
used the repos format version 7), and then, for some external reasons
had to made the move to Debian Jessie. I doubt subversion 1.8 could be
able to read the hot-copies I would have done on the Ubuntu server. Or
would it ? If not, this means repos wouldn't be portable across OS
(while in their most current version at a specified date, for example,
early 2017 for the sake of this example). However, to my
understanding, would I have used dumps to backup my Ubuntu server, I
would have been able to restore the repos. Admittedly, I would have
lost the new functionalities introduced in subversion 1.9, but I still
would have been able to run subversion and access my repos, which
seems not to be the case in the event I would just rely on repos
hot-copies. Or would it ?

I would be really interested to get your view on all this in order to
see if I misunderstand what to expect from the hot-copies and the
dumps, and if my setup is overkill, or if it doesn't meet the
requirements I thought it would.

[1] https://subversion.apache.org/docs/release-notes/1.9

Best Regards,
Received on 2019-08-23 10:16:24 CEST

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