Is it possible to convert an HP MSA20 from U320 to SAS?
Solution 1:
No. It's not possible.
The HP StorageWorks MSA20 is an Ultra 320 parallel SCSI-only device for its external interface. It's a SATA backplane... But remember, it's first-generation SATA; 1.5Gbps. Terrible.
If you want something compatible, you'll need an MSA50, MSA60, MSA70, D2600 or D2700... You get the idea. Something more modern.
Also see the advice given on your previous question: 3.5" SATAs in an HP DL580 G4