Time Machine Not Auto-Deleting Old Backups When Full

This has me a little puzzled...

I'm using a Seagate Backup Plus for T.M. on my new 2012 iMac.

I'm using a 500 GB WD FW800 (purchased circa 2009) with my mid 2008 MBP (model just prior to the unibodies).

Problem is when my Seagate fills up with T.M. backups, it doesn't automatically delete the oldest. It just gives me an error message in T.M. saying it couldn't complete backup because there wasn't enough space on the external HDD. I have to manually delete the oldest one or two backups before it will work. I do not have this issue with the WD on my MBP. Both Macs are on 10.8.2 and have 99% identical apps/docs/photos/etc. The iMac was setup using the most recent MBP T.M. backup.

I just don't know where the problem could lie. I can't conceive how different hard drive brands would make any difference with T.M. not auto-deleting. Is there a setting I'm unaware of somewhere in T.M. preferences?

I just don't know where the problem could lie. I can't conceive how different hard drive brands would make any difference with T.M. not auto-deleting. Is there a setting I'm unaware of somewhere in T.M. preferences?

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No setting that I'm aware of, it should work with any drive. It works for me with a Hitachi, iOmega, and Samsung drives. I don't have a Seagate external.

Does your 2012 iMac by chance have a Fusion drive?

chscag said:

No setting that I'm aware of, it should work with any drive. It works for me with a Hitachi, iOmega, and Samsung drives. I don't have a Seagate external.

Does your 2012 iMac by chance have a Fusion drive?

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No fusion drive. Regular old stock 1TB.

I'm tempted to re-format the external with Disk Utility and start over with T.M. just to see if it clears it up. But I'll save that for the weekend if I don't get any alternative suggestions first.