Verify to Dedup volume slow for one job but not the other

Hi,

I have 2 remote sites backing up to a central site dedup volume.  The data has been pre-seeded.

The backups went well for both sites.  However one site is verifying @29 MB/min while the other site is verifying at 135 MB/min. Why would this be so?  Would it have anything to do with different WAN speeds at the 2 remote sites?  I was told that the verify operation all happens on the central site media server, and that disk I/O is the determining factor for verify speed.  However, this does not explain why 2 jobs with the same settings are performing so differently.

Thanks