[CentOS] Rsync and differential Backups

Tue Nov 10 20:16:28 UTC 2015
Warren Young <wyml at etr-usa.com>

On Nov 10, 2015, at 8:46 AM, Gordon Messmer <gordon.messmer at gmail.com> wrote:
> On 11/09/2015 09:22 PM, Arun Khan wrote:
>> You can use "newer" options of the find command and pass the file list
> the process you described is likely to miss files that are modified while "find" runs.

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.

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.

On the BSD Now podcast, they recently told a war story about moving one of the main FreeBSD servers to a new data center.  rsync was taking 21 hours in back-to-back runs purely due to the amount of files on that server, which gave plenty of time for files to change since the last run. 

Solution?  ZFS send: