[WARNING - do not flash LSI-9201-16i HBA with P20]

Might want to check your p20 subversion. the original release (20.00.00.00) had io bugs according to LSI. There have been more releases 20.00.02.00 and 20.20.04.00. Fixes it according to folks who had issues with this on FreeNAS.

[Xpenology and SAS Controller - HBA]

There are updated revisions of the p20 firmware that fix the issue. v20.00.00.00 had sense or io error issues. fixed current version of p20 is 20.00.04.00

[I/O error occurred to hard disk X]

I ran into this issue with my HBA as well; though on FreeNAS. The initial releases of firmware P20 ( Version 20.00.00.00 ) Used on the LSI 2008 / IBM M1015 etc had some bug that caused io errors or media errors. Lots of freenas community chatter on this issue too. LSI released later updates ( Versions 20.00.02.00 and 20.00.04.00 ) that are supposed to fix this bug.