Hello Leila87, perhaps updating the BIOS and SSD firmware will help.
If the issue persists you may want to provide the operating system and SATA mode being used.
Thanks for your suggestion, bios was already up to date, but drive not, so updating to latest firmware seems to have solved the problem.
Link is now at 6Gb/s, here is a test:
Sequential Read : 493.138 MB/s
Sequential Write : 270.356 MB/s
Random Read 512KB : 398.744 MB/s
Random Write 512KB : 268.910 MB/s
Random Read 4KB (QD=1) : 20.551 MB/s [ 5017.4 IOPS]
Random Write 4KB (QD=1) : 51.009 MB/s [ 12453.3 IOPS]
Random Read 4KB (QD=32) : 188.841 MB/s [ 46103.7 IOPS]
Random Write 4KB (QD=32) : 219.028 MB/s [ 53473.6 IOPS]
Test : 1000 MB [C: 8.4% (20.1/238.4 GB)] (x5)
Date : 2014/06/20 19:54:54
OS : Windows 7 Ultimate SP1 [6.1 Build 7601] (x64)
mSATA 256GB CRUCIAL 20-06-2014
I suppose this is now ok? the average speeds i should be getting for sata 3?