9264: Acronis Drive Monitor: Disk Health Calculation

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Last update: 22-11-2013

Disk health calculation by Acronis Drive Monitor


Why calculate disk's health status?

The calculated hard drive's health shown as percentage provides you a better visual representation of S.M.A.R.T. related problems.

Health status warns you of disk degradation, when S.M.A.R.T. reports a problem.

This will help you to protect your data before your disk fails.

How to calculate disk's health?

Critical parameters:

Initially a hard disk has 100% health condition.

All S.M.A.R.T. parameters considered by Acronis Drive Monitor as critical for a hard drive (if they are available for monitoring, it depends on the manufacturer), decrease the calculated health status of your disk. Such attributes have a predefined weight and a maximum limit value (see a Table 1 below).

A limit defines how much the attribute may decrease an overall health value. A weight of an attribute defines how important the parameter's value decreasing the affected the disk's health.

The overall disk health is calculated by the formula below:

Disk health (%) = П (100% - (min(limit, attribute_value*Weight)))


  • 100% - initial health of the disk;
  • П - the product of minimums from (limit, attribute_value*Weight) - calculated for each critical S.M.A.R.T. parameter;
  • Weight - weight of each critical S.M.A.R.T. parameter (see a Table 1 below);
  • limit - limit of each critical S.M.A.R.T. parameter (see a Table 1 below);
  • attribute_value - current parameter's value.


  • Soft Read Error Rate = 30 (attribute value), weight = 1, limit = 20;
  • Spin Retry Count = 12 (attribute value), weight = 2, limit = 50.
  • So in this case the disk's health is calculated as the following:

Disk health = (100% – (min(30*1, 20))) * (100-min(12*2, 50))) = 80%*76%=60.8%≈61%

The following table contains the health related (critical) S.M.A.R.T. attributes affecting the health value with their weights and maximum limits.

Table 1.

Attribute ID S.M.A.R.T. attribute Weight Limit %
05 Reallocated Sectors Count 2 70
10 Spin Retry Count 2 50
184 End-to-End Error 1 50
196 Reallocation Event Count 1 40
197 Current Pending Sectors Count 1 40
198 Offline uncorrectable Sectors Count 2 70
201 Soft Read Error Rate 1 20

Not critical parameters:

Other S.M.A.R.T. parameters, which have a predefined by manufacturer threshold value, also affect disk's health: after decreasing below the threshold, this parameter subtracts 10% from the current disk health. This means, when the current health is 90%, 9% will be subtracted.

Table 2 shows non-critical S.M.A.R.T. parameters, that affect disk’s health.

Table 2.

Attribute ID S.M.A.R.T. attribute
01 Raw Read Error Rate
02 Throughput Performance
03 Spin Up Time
04 Start/Stop Count
07 Seek Error Rate
08 Seek Time Performance
09 Power-On Time Count
12 Drive Power Cycle Count
221 G-Sense Error Rate
228 Power Off Retract Cycle
225 Load/Unload Cycle Count
194 Disk Temperature
199 Ultra ATA CRC Error Count
193 Load/Unload Retry Count

What else may decrease disk's health?

When a disk is monitored using a custom script:

exit code is 0 : Health = (disk health calculated by S.M.A.R.T.) * 100%
exit code is 1 (warning): Health = (disk health calculated by S.M.A.R.T.) * 50%
exit code is 2+ : Health = 0%

Factors not affecting disk’s health

  • Decreasing value of a non-critical parameter does not affect the disk’s health until it is above a threshold, specified by the disk's manufacturer;
  • Event log entries also do not change the overall disk health, but still can generate Warnings or Errors.

More information

See also: