Time Machine backups way too big

Has anyone else experienced anything like this?

I’m using a Macbook Pro that uses Time Machine to wirelessly backup to my Drobo 5N. Every time TM backs up, I see that the back up size is always about 21-25 GB, which is far more than it should be. My Mac Pro, on the other hand, which is hardwired to the same router as the 5N, shows normal sizes when backing up. The sparse bundle dmg file on the 5N’s Time Machine partition for my Macbook Pro shows a size virtually the same as the space used on my MBP. Therefore, I don’t think my Macbook’s backups are actually taking up too much space, though I do think my 5N’s partition is depleting in space faster than it should.

If anyone has experienced this, please let me know if this is normal for some reason or if you know how it can be fixed

How much data is there on your MacBook Pro’s hard disk? Time Machine does a sanity check before making an incremental backup and if it finds a problem it starts over with a full backup. Could that be what’s happening in your case? I’ve seen this happen when using a network share as Time Machine’s destination and I traced the problem to the fact that, like you, it was trying to work over a WiFi connection. WiFi is much less reliable than people would like to believe, especially in the overcrowded 2.4GHz band. Try connecting it with an Ethernet cable instead and see if that makes a difference. If it does, you might try relocating your wireless access point or switching to a less crowded channel, perhaps in the 5GHz band. Better still, stick with the cable.