HDD in caddy not working corectly

[snipeman]

Hi.  My original 500 GB HDD was replaced by 120 GB SSD, and was installed using  a caddy in place of the optical drive. The problem is that the HDD (SSD too!) works too slow from the caddy?! Saying "slow" I mean that the transfer speed do not exceed 7-8 MB/s, and every 40-50 seconds it drops down to 0 MB/s for about 10 sec. or more?! I've install 80 GB in the caddy and it works just fine on the laptop?! At first I was thinking it is the caddy that's causing problems - probably not able to handle drives larger than 80 GB?! Then I install the caddy with the 500 GB HDD in my other PC - Dell Optiplex SFF and it works just fine?! Is there some hardware limitations of the 255 G4 or do I need to change something in BIOS?! 

[Huffer]

An optical drive caddy provides very limited performance as the port is a limited performance SATA port. How exactly do you have it set up? You should put the SSD inside the laptop in the 2.5 inch bay and the HDD in the optical caddy but understand transfer speed will be capped. 

[snipeman]

SDD is inside the laptop's 2.5" bay and the HDD is in the optical caddy. With the 80 GB HDD it gets a transfer speeds of at  least 25 MB/s and there is no dropdowns?! With 500 GB HDD it starts from 200+ MB/s for 10-20 sec. After that it drops to 0 MB/s. for lets say 10 sec, gets up to 8 MB/s. for lets say 40-50 sec. and so on...