Sincere thanks to everyone for their replies. Before following some of the advice offered I decided to investigate the machine filesystem further.
I'm no linux expert (obviously :)) but found that of the ext3 filesystems on each disk, the dir_index feature was only enabled on the primary disk. Research revealed that this helped with directory listing and it made sense that with 1mill files in one directory, it might be a good idea to have it enabled on both disks! Result: The local backup completes in <10min instead of 1hr20min+. It also explains why local primary disk to remote primary disk backup was fast, as both these had dir_index enabled. On CentOS at least, additional mounted ext3 drives don't seem to have dir_index enabled by default. It's a massive relief to have this finally sorted, I've spent far too many hours trying to fix it. I don't know whether this might be a useful tip in the Rsync FAQ troubleshooting when backing up large directories of small files. -- To unsubscribe or change options: https://lists.samba.org/mailman/listinfo/rsync Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html
