Windows 7 Backup running VERY slowly, ran fine last month

I am backing up to an 3TB ESATA drive using Windows 7 Ultimate x64 w/SP1. I run backups monthly and last month the backup ran normally. This month however when the actual writing of the zip files to the backup drive began it slowed to a crawl. It actually appears to have stalled with only occasional disk activity either from the drives being backed up or the destination drive. I have run chkdsk on all drives (source and destination), sfc, checked error logs, CBS.log, and done a clean boot but the situation has remained unchanged.

When I look at the backup folders on the destination drive I find that my previous backup that ran normally builds 4 or 5 zip files per minute. My current backup that has been running for over 12 hours is only creating one zip file per hour approximately! Something is seriously wrong. CPU activity is at or near idle and as I mentioned there is very little and only occasional disk activity. Not at all what I see when backup is running normally.

I originally thought backup was hanging or stalled at 12%. I did find one error the first time through this round of backing up and that was related to the renaming of SkyDrive to OneDrive. I uninstalled OneDrive and tried running backup again, same experience. It wasn't until I looked at the backup folders on the destination drive that I realized it was running but very slowly.

I have also found that when backup is running my destination drive is slow to display folders. I have run a chdsk /f/r on it (without backup running) and that proceeded speedily without errors. Without backup running files copy to/from the destination drive quickly as well.

I have seen lots of threads about backup running slowly but no real answers. I hope some of these extra details I have provided can point to a possible cause and solution.

Danno

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