After installing Yosemite, boot takes too long

Hi,

I have a MacBook Pro late 2011 (17") and my factory hard disk gone down (I was using Maverick).

I installed an Hybrid Toshiba hard drive (8 Gb SSD / 1 Tb HDD) and also Yosemite.

Everything works fine, but the boot hangs for a while on the apple logo before continue to login screen.

If I clean the PRAM, the boot is at least 1 minute faster. This speed may survive one or two extra restarts. After that it's really slow again, until I reset PRAM again.

Is there any way of monitoring what wrong the OS is trying to write on PRAM and control this without having to clean PRAM every day?

Thanks.