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Re: CUT rolling release debian BUT a cautionary comment

On Sat, Mar 07, 2015 at 12:56:31AM +0100, Adam Borowski wrote:
> On Fri, Mar 06, 2015 at 03:26:32PM -0700, Paul E Condon wrote:
> > you should have at least two computers running Debian, and be able to
> > spend a few hours or days with one of them non-functional, for the
> > following reason:
> Or, use btrfs.  Put your / onto a subvolume named sys-current, and have the
> following cronjob:
> # btrfs subv snap sys-current backups/sys-`date +%Y-%m-%d`

Michael Vogt wrote some time ago apt-btrfs-snapshot as POC which hooks
into apt directly to create the snapshots automatically on every
system-changing interaction. [0]

If I remember correctly btrfs mostly showed its ugly experimental
state by being very slow which is hard to justify in an environment
where everyone already complains how slow upgrades are in Debian.
Hopefully its better now…

The idea was to add some grub magic as well so that a user can easily
pick an older snapshot if need be and then sell it big time as our
transaction safe and backrollable apt. So, in case anyone is interested,
head over to deity@l.d.o and lets talk business. ;)

[0] https://bazaar.launchpad.net/~mvo/apt-btrfs-snapshot/trunk/files

> [2]. Besides separate /home (duh), you'll want to reduce the size of backups
> by separating out /var/cache, make sure noatime is set, etc.

I don't think /home is such a no-brainer. Sure, this is sold for cases
in which a system doesn't boot anymore, but that rarely ever happens.
People are much more likely to use it to revert back from Z20 to Z19,
but Z20 will have converted all config files already, so Z19 is now
crashing. Now combine this with someone who actually came to terms with
Z20, but three weeks later discovers that feature X is broken, which he
used like 2 months ago the last time, but absolutely needs it now, so
that we revert now 2 months instead of painfully bisecting where it
broke (last week)…

So in an ideal world /home would not be separate – or at least not if
you keep /etc on / as well – but your data. Whatever that is…
'What do you mean "incompatible savefile"? That was the run of my life!'
(insert databases, mails, websites and vdr record timers here)

That is hardly a btrfs problem per se, but if you are selling it as the
way to end all (system) backups, users will run into it sooner or later
and be very disappointed – and backups shouldn't be disappointing…

Best regards

David Kalnischkies

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