[Zope] backup full instances

[Jonas Meurer]

On 27/10/2007 Andreas Jung wrote:
>>> If you create a local copy, it is safe. If you rsync a running Data.fs,
>>> it  is not safe. In this case you create a local copy and rsync the copy.
>>
>> but if rsync is unsafe only because it takes long time, and changes on the
>> instance during the copy process could cause a corrupted Data.fs to be
>> backuped, then theoretically this could happen for a local copy as
>> well, right?
>
> Think twice about your last sentence. What should cause a local *copy*
> to be changed??

zope might write to the Data.fs while it is copied, thus an inconsistent
copy would be backuped, even inside one filesystem.

i've asked in #debian on freenode as i wasn't sure, here's the log:

< mejo> if i copy a large file inside a mounted filesystem (ext3), is it
	possible that the file is changed during the copy process?
< Wyzard> mejo: Yes, it's possible that something else can write to the
	file while you're copying it
< mejo> because i asked on the zope-users mailinglist if i could backup
	the global Data.fs (database) while the daemon is running, and
	someone answered:
< mejo> If you create a local copy, it is safe. If you rsync a running
	Data.fs it  is not safe. In this case you create a local copy
	and rsync the copy.
< Wyzard> mejo: Making a local copy is faster, so it'd be safer, but
	still not completely safe
< mejo> exactly, that's what i thought as well.
< mejo> but when i wrote that, he replied:
< mejo> Think twice about your last sentence. What should cause a local
	*copy* to be changed??
< mejo> so he's wrong?
< Wyzard> I'd say he's wrong
< Wyzard> A local copy isn't instantaneous, and Zope changes the file
	while it's being read
< wols_> he is wrong yes
< mejo> thanks. is it ok for you if i quote you in my reply mail?
< Wyzard> mejo: sure
< wols_> mejo: while copying zope could change the database and create
	an inconsistent state

greetings,
 jonas
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