Read surface tests show varying slow blocks

[jelson]

Just finished decommissioning the HDD from a retired Vista laptop where a single bad sector was fixed during the first reinitialization. Steps:

• Read surface test
  Reinitialize disk surface (1 bad sector corrected)
  Reinitialize disk surface
  Read surface test.

As I looked over the screenshots of results, I couldn't help wondering why different blocks would show up as "slower" in different surface scans. It seems to me that a "slower" block would be consistently "slower" instead of changing. For example, this is the 1st Read scan:

1st Read scan

20170205_R_WDC_WD2500BEVT-75ZCT2_-surface-full.jpg (576.16 KiB) Viewed 4149 times

After two single pass Reinitialize disk surface tests, I did a 2nd Read scan:

2nd Read scan

20170206_R_WDC_WD2500BEVT-75ZCT2_WD-WXH808A49177_-surface-full.jpg (583.16 KiB) Viewed 4149 times

NOTE: the results from both the Reinitialize disk surface tests had different blocks showing up as slower. Doesn't seem to be any pattern here.

P.S. Just in case it's relevant, here's the scan from the 2nd Reinitialize scan (The 2nd Read test was done after this):

2nd Reinitialize scan

20170206_RI_WDC_WD2500BEVT-75ZCT2_-surface-full.jpg (583.68 KiB) Viewed 4149 times

[hdsentinel]

The most important is that the slower blocks do not form continuous, larger areas and there are no really slow (very dark) blocks.

Generally background activity of the OS, other applications (and sometimes other devices) may affect monitoring of the performance during the disk test.
Hard Disk Sentinel locks the drive for exclusive use and does everything to minimise this - but there can be other factors which may result in slight performance drops. Other devices/disks connected to the same controller share the total bandwidth and using other devices may affect the result of the drive tested (for example other USB drives on the same USB controller).

This is completely normal and acceptable, the important is that the appropriate sector repaired by the test and that the newer test(s) show no yellow / red blocks.

[jelson]

Thank you... wasn't sure how to interpret the results