Can you post more details about the T420 and the crucial drive model ? How are you measuring speed ?
So far I have found no crucial SSD /SATA-3 that claims more than 415MBPS in sustained sequential reads.
FWIW the Micron/Crucial M4 (C400) series (which I assume you have) are pretty sweet.
But the technical review here shows 404.8 MBPSon sequential reads - close to the mfgr's 415 MBPS claim.
To get 500 MBPS or even 400, you'd need SATA-3, but a limit of ~300MBPS is about where SATA-2 stops. So this brings into question exactly how your interface is configured in the two kernels.
I *think* that if you do this command on both OSes you might see a difference.
sudo hdparm -I /dev/sda
Go ahead and post the results (I'd like to see 'em - curiousity).
My SATA-2 drive has the following lines of output ...
* Gen1 signaling speed (1.5Gb/s)
* Gen2 signaling speed (3.0Gb/s)
and I expect you will get a 6Gb/s line. Note that the '*' asterisk indicates the feature is enables, or available.
Have you tried a 3.1 kernel ?
---------- Post added at 04:21 AM ---------- Previous post was at 04:04 AM ----------
I just found that you should gt a message ....
* Gen3 signaling speed (6.0Gb/s)
But the F14 hdparm is too old to contain this. You need