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On 10/11/15 21:05, Gordon Messmer wrote:
> On 11/10/2015 12:16 PM, Warren Young wrote:
>>
>> Well, be fair, rsync can also miss files if files are changing
>> while the backup occurs. Once rsync has passed through a given
>> section of the tree, it will not see any subsequent changes.
>
> I think you miss my meaning. Consider this sequence of events:
>
> * "find" begins and processes dirA and then dirB * another
> application writes files in dirA * "find" completes * a new
> timestamp file is written
>
> Now, the new file in dirA wasn't seen by find during this run, and
> it won't be seen on the next run either. That's what I mean by
> missed. Not temporarily missed, but permanently. That file won't
> ever be backed up in this very naïve process.
That's plain bad system analysis. Read the start date, record the
current date and THEN start processing. You will get the odd extra
file but will not loose any.
>
> There's no benefit to the process, either. rsync can efficiently
> examine and synchronize filesystems without using find. And while
> it may miss files that are written while it's running, it *will*
> get them on the next run, unlike using "find".
>
>> If you need guaranteed-complete filesystem-level snapshots, you
>> need to be using something at the kernel level that can
>> atomically collect the set of modified blocks/files, rather than
>> something that crawls the tree in user space.
>
> Generally, I agree with you. In fact:
> https://bitbucket.org/gordonmessmer/dragonsdawn-snapshot
> https://github.com/rsnapshot/rsnapshot/pull/44
>
> Doing block-level differentials is nice, if you're using ZFS. But
> not everyone wants to run ZFS on Linux. I do think that backing
> up snapshots is important, though.
>
> _______________________________________________ CentOS mailing
> list CentOS@xxxxxxxxxx
> https://lists.centos.org/mailman/listinfo/centos
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