The problem of SMART-data ambiguity in different models of hard disk drives of the same manufacturers is considered. This circumstance creates obstacles for the use of SMART technology when assessing and predicting the reliability of storage devices. The scientific task of the work is to study the dependence of the hard disk failure probability on the reliability parameters values for each individual storage device of any model of any manufacturer. In the course of the study, two interrelated parameters were analyzed: “5 Reallocated sectors count” and “9 Power-on hours” (the number of hours spent in the on state). As a result of the analysis, two types of dependences were revealed: drooping and dome shaped. The first means the maximum failure frequency of information storage devices immediately after commissioning, the second - after a certain period of time, actually coinciding with the warranty period for the products (two years). With the help of clustering in plane according to the coordinates of the number of reallocated sectors and the time of operation, two different reasons for the failure of the drives were discovered: due to deterioration of the disk surface and due to errors in the positioning of the read / write heads. Based on the variety of types of causes and consequences of equipment failure, the task of individual assessment of an individual data storage device reliability is proposed to be solved using several parameters simultaneously.

The data ambiguity problem for heterogeneous sets of equipment reliability indicators is considered. In fact, the same manufacturers do not always unambiguously fill the SMART parameters with the corresponding values for their different models of hard disk drives. In addition, some of the parameters are sometimes empty, while the other parameters have only zero values.The scientific task of the research consists in the need to define such a set of parameters that will allow us to obtain a comparative assessment of the reliability of each individual storage device of any model of any manufacturer for its timely replacement.The following conditions were used to select the parameters suitable for evaluating their relative values:1) The parameter values for normally operating drives should always be greater or lower than for the failed ones;2) The monotonicity of changes in the values of parameters in the series should be observed: normally working, withdrawn prematurely, failed;3) The first two conditions must be fulfilled both in general and in particular, for example, for the drives of each brand separately.Separate averaging of the values for normally operating, early decommissioned and failed storage media was performed. The maximum of these three values was taken as 100%. The relative distribution of values for each parameter was studied.Five parameters were selected (5 – “Reallocated sectors count”, 7 – “Seek error rate”, 184 – “End-to-end error”, 196 – “Reallocation event count”, 197 – “Current pending sector count”, plus another four (1 – “Raw read error rate”, 10 – “Spin-up retry counts”, 187 – “Reported uncorrectable errors”, 198 – “Uncorrectable sector counts”), which require more careful analysis, and one (194 – “Hard disk assembly temperature”) for prospective use in solid-state drives, as a result of the relative value study of their suitability for use upon evaluating the reliability of data storage devices.

The change of the SMART parameter 10 Spin retry count values depending on the operating time is considered; this parameter characterizes the number of repeated attempts to spin the disks up to operating speed if the first attempt was unsuccessful. This parameter is critical in the sense that if the value of the attribute increases, then the likelihood of malfunctions in the mechanical part of the hard disk drives is high. The scientific task of the study is to establish the relationship between this parameter in failed hard drives and the values of other reliability parameters for information stores from various manufacturers. In the course of the study, the drives of the HGST, Hitachi, Samsung, ST, Toshiba, WDC trademarks operated in the Backblaze largest commercial data centre were analysed. As a result of the analysis, the relationship between the specified parameter and such parameters as 3 Spin-up time (time of spinning the disk package from standstill to operating speed), 4 Start/stop count (counting the spindle start/stop cycles), 12 Power cycle count (number of full drive switching on/off cycles), 192 Power-off retract count (the number of shutdown cycles, including emergency), 193 Load cycle count (the number of magnetic head block moves in the parking zone/in working position cycles). It is shown that the nature of the change in the values of the considered parameters depends on the manufacturer of the hard drives. It is proposed to carry out an individual assessment of the information storage device rotation mechanism reliability using the parameters identified as a result of the study.

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