Adjusting AFH Values Via Terminal

CAUTION!!! ADJUSTING AFH VALUES MAY RESULT IN MEDIA DAMAGE/CRASHED HEADS, RISKING PERMANENT DATA LOSS!!!

Note- For this first experiment we did not use ZOC scripting; each parameter change was issued manually via terminal.

My workmate and I decided to give this a try after letting a Seagate Pharaoh drive suck up hours upon hours of time on the PC3K while attempting to image with a degraded head 1. We know this process is still very experimental with mixed results. However we had already recovered the data needed from this drive and the case had been closed, leaving us less concerned about the risks. I agree with many others’ statements regarding the process of adjusting temperatures (or any other critical system values) in an HDD. There are too many variances in each case to decide yet if this is a reasonable solution for all drives.

The first step in AFH adjustment via terminal commands is to gain level 7 access and issue the following command: I,1,f,1 . This is to view the current RAP/AFH specific to the target head (in this case, we are targeting the degraded head 1). You will see many other parameters that could be adjusted, such as W+HtClr (Write Height Clearance), but I have only experimented with RHtClr. Once you have the values of each parameter you need to alter, you send that command and factor in the incremented 0x value right after ‘I‘. Other data recovery folks have mentioned incrementing by 10 or 20, but to err on the safer side we started with a meager 5. We continued incrementing by 5 noting any variance until we capped at an increase of 25.

The initial AFH increase of 5 resulted in an increased speed from 6.4KB/s to 12.7KB/s with an extremely low average of 4.3KB/s. With an increment from 5 to 10 the speed reached 215.3KB/s. From 10 to 15 there was a slight increase from 215.3KB/s to 255.4KB/s. When we increased from 15 to 20 we noticed a much more significant difference in speed from 255.4KB/s to 6.0MB/s, and at our final increment to 25 the speed increased from 6.0MB/s to 15.5/MB/s with an average of 12.2MB/s.
In my experience this tactic does seem to work to increase imaging speed for a degraded head in a Seagate Pharaoh. I plan to keep trying this solution on different drives and documenting the results. As many others have mentioned, more research is needed.

How to adjust AFH values in order to increase read speed and imaging process and avoid physical repair such as a head swap:

In our lab we begin incrementing 0x parameter by 5 until desired effect is reached.  Parameters must be altered separately for each zone (meaning the command formula must be manually sent for all zones, changing only P5 with each command sent, and accounting for the incremental value that is reflected in the 0x parameter.  User must also account for each drive family’s incongruous and seemingly random value assignments to each parameter e.g. in Pharaoh drives, P1= 1, P2= f, P3= target head 0-y, P4= 4, P5= zone geometry as a hex value e.g. 0x00.  The generic command formula for Pharaoh HDD AFH adjustment is as follows:  F3 7>I0x,P1,P2,P3,P4,P5

Each command parameter is described below:

  • I= terminal command (at level 7)
  • 0x= hexadecimal value that is being altered (in this case it is RHtClr or Read Height Clearance)
  • P1= parameter 1; RAP (Read Adaptive Parameters)
  • P2= parameter 2; RAP AFH Head/Zone parameters
  • P3= parameter 3; target head
  • P4= parameter 4; parameter to be targeted, in this case it is the RHtClr
  • P5= parameter 5; the target zone

example:  F3 7>I85,1,f,1,4,00

The above example is the command that would be issued in order to change the original RHtClr of Head 1 from 0x7B to 0x80 for an initial increment by 5 while adjusting the RAP in Head/Zone parameters ‘f‘ for head 1 in the target zone 00.

Notes on AFH Values
Head Speed After Adjustment

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