Hard Disk Sentinel Help - Health calculation

It is possible to select many different health (condition) calculation methods at the advanced options. The differences between these evaluation methods:

Analyse data field

If this option is selected, the raw, measured numbers (displayed in the Data column for the corresponding S.M.A.R.T. attributes) are used to determine hard disk health. When developing the calculation method, the following aspects were important:

• It should reflect the actual status. Should not depend on time or past values. Determine the result without using long time analysing or testing methods.

• It should not increase with time - do not show the health status better after some time (except if some pending sectors were successfully tested and they can be used because they have no problems).

• It should reflect small changes and degradations. Constantly increasing number of problems should constantly decrease the result.

• It should count the relationship between attributes. More different problems should decrease the result much drastically than only one single problematic attribute.

• The result should be same for two (or more) hard disks with the same problems, even if the hard disks are from different models, manufacturers.

• The result should be controlled in some situations. For example after replacing a problematic power supply, the problems encountered previously should be ignored. Also an improper sensor should be ignored or its value should be modified (please see temperature calibration about this).

The hard disk has 100% condition initially. All critical health-rated S.M.A.R.T. parameters (if they are available, it depends on the manufacturer) decrease this value. These attributes have a pre defined weight and a maximum limit value (the latter defines the maximum degradation in health value for the attribute). The overall health percent value is calculated by multiplying the remaining percent values (100 - degradation %).

Currently, Hard Disk Sentinel has two different such methods. By using the default method, the weights and limits (see below) are lighter. If the more strict, recommended for servers option is used the values are much more strict, the problems may reduce the health much drastically.

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

Weights and limits for the default calcuation method:

S.M.A.R.T. attribute	Weight	Limit %
Reallocated sectors count	1	70
Seek error rate	0.5	20
Spin retry count	3	60
Reallocation event count	0.6	30
Current pending sectors count	0.6	48
Off line uncorrectable sectors count	1	70

Weights and limits for the more strict calculation method:

S.M.A.R.T. attribute	Weight	Limit %
Reallocated sectors count	6	60
Seek error rate	2	20
Spin retry count	6	40
Reallocation event count	4	30
Current pending sectors count	4	30
Off line uncorrectable sectors count	6	60

The numbers are determined by examining the arrived reports and the S.M.A.R.T. status of (unusable) hard disks received for data recovery.

Note: the Data column contains hexadecimal values. These should be converted to decimal before calculation. The lower 16 bits (righmost 4 digits) are used in the calculation method.

For example: using the default calculation method. If the "Reallocated sectors count" attribute has 0002 in the "Data" column, the health value = 100 x ( 100 - 2x1 ) % = 98 %

If the "Current pending sectors count" attribute has 0005 in the "Data" column also on the same hard disk, the health is = 98 x ( 100 - 5x0.6) % = 95 %. The more strict calculation method gives 100 x (100 - 2x6) % x (100 - 5x4) % = 70 % as the resulting health value.

The limit % defines how much % can the attribute decrease the overall health value. For example, if the "Off line uncorrectable sectors" attribute contains 0200 in the "Data" column (which is 512 if converted to decimal value), the heatlh should fall by 512 x 1 = 512 %, but the limit for this attribute is only 70 %. With other words, if the value of the "Off line uncorrectable sectors" is high, the health value of the disk cannot be larger than 30 %. Other problems may decrease the health value more.

Analyse vendor specific values

If this option is selected, the health-related S.M.A.R.T. attributes are evaluated. All such attributes will have a small condition value calculated between 0 and 100% based on the actual value, the threshold and the theoretical maximum value (the latter is determined by Hard Disk Sentinel based on the manufacturer and model). Multiplying these values will give the overall health of the hard disk condition.

For example: the threshold for the "Reallocated sectors count" is 36, the value is 84 and the initial value for this attribute was 100. The condition value for this attribute is: (1 - (100-84)/(100-36)) x 100 = 75 %. If (on the same hard disk) the threshold for the "Seek error rate" is 30, the value is 60, and the initial value is 90, the condition of this attribute is 50 % and the overall health of the hard disk is 37.5 %.

Note: 1.40 and previous versions of Hard Disk Sentinel had only more strict, recommended for servers calculation method. Upgrading from 1.40 or older version may result in a different health value display. On the advanced options page it is possible to modify the calculation method any time.

Note: the selected calculation method is saved into the reports to prevent confusion.

Note: usually the different health values follow the formula:

Vendor specific >= Default >= More strict

By using the "more strict" method, the health value decreases drastically in case of any small problem, so the use of this method is recommended only when no (even small) problem is allowed.

SSD Health

Memory cells in solid state devices (generally flash storage) can tolerate only limited number of overwrite passes, so experience "wear" during normal use.

The "wear-leveling" feature of the SSD tries to hide/minimise this effect but generally it can't be eliminated. Usually the SSD device maintains an overall health of the memory cells and provides this information by various attributes.

If no problems found, Hard Disk Sentinel reads such attribute(s) to determine the complete health of the solid state device and displays in the text description: The health is determined by SSD specific S.M.A.R.T. attribute(s):

Such attributes can be #177 Wear Leveling Count, #231 SSD Life Left, #233 Media Wearout Indicator, Percentage Used, Remaining Drive Life or similar. On the S.M.A.R.T. page, it is possible to examine the current value and also change with time.

Such values (and thus the health) is calculated by the SSD, independently from any software, based on the actual usage: amount of written data, power on time and so. To keep the health high, try to minimise the amount of data written to your SSD.