Time Machine backup extremely slow after upgrade to Yosemite

I recently updated my MacBookPro from Mavericks to Yosemite and found that Time Machine backup speed has really slowed down.

I realized the amount of new/changed files jumped quite a bit after the upgrade, so I expect the first backup to take a while. However, the backup speed seem unusually slow.

I let it run overnight and in 12 hours it copied 18GB out of 500GB, for an effective transfer rate of about 0.025 GB/min. At this rate it will take something like 14 days to complete.

For comparison, and to make sure the external drive and USB ports were basically happy, I copied a 4GB file over to the external drive manually and it measured at 8.5 GB/min (very fast).

Has anyone else seen this and/or have any suggestions for troubleshooting?

My system:

• MacBookPro, retina, 15-in, late 2013


• 2.6GHz i7


• 16 GB RAM


• 500 GB SSD


• Seagate Backup Plus Slim portable drives, USB 3.0 (1TB and 2TB)