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Re: [Bacula-devel] Using the OS to get the list of files changed
>>>>> On Sun, 12 Oct 2008 11:21:12 -0400, Dan Langille said:
> With incremental and differential backups, the goal is a list of files
> that have changed since a given point in time. Traditionally, this
> list is obtained by using find (AFAIK). On filesystems with large
> numbers of files,the list creation can take considerable time. How can
> we improve the performance of this stage?
> For some time, I have wanted the filesystem (or OS) to give me a list of
> files changed since time X. I've just heard Pawel Jakub Dawidek speak
> at NYCBSDCon about ZFS. I asked him if he thought getting such a list
> was possible. He suggested it may be. Strategy: ZFS is able to return
> a file name given a particular block. That is, if you know a particular
> block has changed, ZFS will tell you what file it belongs to.
> When using ZFS snapshots, the system keeps a list of blocks that have
> changed since the last snapshot. It may be feasible to traverse this
> list of block to obtain the list of files required by Bacula.
> My thoughts:
> 1 - I'm not proposing to apply this strategy to Bacula internally.
> However, an external script would be very useful. Bacula already
> provides a mechanism for a FileSet to be specified by an external
> script. I'm thinking: combine the two approaches to provide faster
> incremental/differential backups.
> 2 - This strategy may be applicable to other filesystems that provide
> similar mechanisms (list of blocks changed, getting file names for those
> blocks). It was suggested during the talk that auditing, etc may
> provide the needed hooks.
A similar idea is used by Apple to implement Time Machine.
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