[CentOS] HDD badblocks

Hi list,
I've a notebook with C7 (1511). This notebook has 2 disk (640 GB) and 
I've configured them with MD at level 1. Some days ago I've noticed some 
critical slowdown while opening applications.

First of all I've disabled acpi on disks.


I've checked disk for badblocks 4 consecutive times for disk sda and sdb 
and I've noticed a strange behaviour.

On sdb there are not problem but with sda:

1) First run badblocks reports 28 badblocks on disk
2) Second run badblocks reports 32 badblocks
3) Third reports 102 badblocks
4) Last run reports 92 badblocks.


Running smartctl after the last badblocks check I've noticed that 
Current_Pending_Sector was 32 (not 92 as badblocks found).

To force sector reallocation I've filled the disk up to 100%, runned 
again badblocks and 0 badblocks found.
Running again smartctl, Current_Pending_Sector 0 but Reallocated_Event 
Count = 0.

Why each consecutive run of badblocks reports different results?
Why smartctl does not update Reallocated_Event_Count?
Badblocks found on sda increase/decrease without a clean reason. This 
behaviuor can be related with raid (if a disk had badblocks this 
badblock can be replicated on second disk?)?

What other test I can perform to verify disks problems?

Thanks in advance.