How Hard Disk S. M. A. R. T. Works? Some time ago an article published about hard disk reliability and the failure prediction function of hard disks. We can think that this function is not working or not too reliable because it is not able to predict disk failure in all cases. It may be partially true - but the situation is not too simple. Note: This operating system may be installed over previous versions of Windows XP and Windows Vista by completing a clean installation, or Windows 7, and Windows 8.1. Data is distinct pieces of information, usually formatted in a special way. All software is divided into two general categories: data and programs. Complicated Fix: To disable Autorun for good in XP/Vista, you need to edit the Registry. As always, before you edit this database, it's smart to make a backup of it. Now, we want to make things clear. First, we examine what is S. M. A. R. T. Advanced users may skip some paragraphs. S. M. A. R. T. S. M. A. R. T. It was created to monitor the disk status by using various methods and devices (sensors). A single ATA hard disk may have up to 3. Some of them directly or indirectly affect hard disk health status and others give statistical information. Today all modern IDE/Serial ATA/SCSI hard disks have S. M. A. R. T. It is not really a standard - so the meaning of the attributes may be different from manufacturer to manufacturer. In this article, we discuss ATA (IDE and Serial ATA) hard disks only. This is because, and this is by design, all virtual machine disk files (VMDK) are presented from Virtual hardware 7 (the one of ESX 3.5) to VMs as SAN disks. Vista Forums x64 is your Vista Forum for everything relating to Windows Vista 32 bit and 64 bit. You can receive free help in our Vista Forums, Vista Tutorials, and. The rotational mechanism in an optical drive differs considerably from that of a hard disk drive's, in that the latter keeps a constant angular velocity (CAV), in. SCSI hard disks work differently: the failure predicition data is standard and there are strict rules about the sensors and algorithms. For example, the difference between real temperature and the result measured by the sensor should be less than +/- 3 Celsius degrees. Many attributes are used by all manufacturers and they are used in the same (or near same) way. That's why for example it is possible to detect the temperature and the total power on time of many hard disks. Newer applications are able to detect, process and display these information. According the S. M. A. R. T. But in many cases this time is not enough - that's why it is important to recognize problems and prepare before it's too late. Click here to see the full list of S. M. A. R. T. The measured values are then processed by some algorithms and the corresponding attributes are modified according the results. A single S. M. A. R. T. Many attributes have standard meanings (for example, 5 = number of reallocated sectors, 1. Most applications provide name and textual description about the attributes. Data (6 bytes): raw measured values are stored in this field, provided by a sensor or a counter. This data is then processed by an algorithm designed by the hard disk manufacturer. Sometimes different parts (for example, low, middle, high 1. Threshold (byte): the (failure) limit value for the attribute. Value (byte): the current relative . This number is calculated by the algorithm, using the raw data (see above). On a new hard disk, this number is high (a theoretical maximum, for example 1. Worst (byte): the worst (smallest) value ever found in the previous lifetime of the hard disk. Status flags: indicate the main purpose of the attribute. An attribute can be for example critical (able to predict failure) or statistical one (does not directly affect condition). Note: software may display more information based on these fields (for example, the status of an attribute, which can be . If this is not true for a critical attribute, failure is predicted, the hard disk is considered bad and it should be replaced immediately (the attribute determines the problem). The S. M. A. R. T. If the Threshold is 0 for any attribute, that attribute is not able to predict failure (because the Value cannot be less than 0). Mathematically, one attribute is perfect if the following inequality is TRUE (you may skip this paragraph if you hate maths): A - f(r) > = C (1) Where: A - theoretical maximum value, the . Usually it is a linear function, so in most cases r is multiplied by a B constant. C - the vendor specific threshold level, under this level, the attribute is considered problematic. This method has some disadvantages. The A, B, C, values (or the f function) are not defined exactly (these may vary from model to model even on two hard disks from the same manufacturer). Other disadvantage is that the attributes are evaluated independently, the relationship between them is ignored. The problems with S. M. A. R. T. The model described above has many weak points. Because of these problems, in most cases failure prediction is not working at all. The major problems are: #1 Incorrect thresholds. Most problems with S. M. A. R. T. Because of this, the hard disk attributes have no chance to reach the thresholds - usually they fail (become useless) before reaching this point. In such cases, S. M. A. R. T. For example, on most hard disks, many thousands of bad (not readable and writable) sectors required (according to the size of the spare area) before S. M. A. R. T. It does not seem to be a big problem because 1. For example, a head problem which can make many thousands of sectors unusable (bad), can cause bigger parts of the disk surface unreadable - preventing the recovery of data from this disk area. Also analysing a such problematic area and saving the data to spare area may need lots of time (even hours), and it is possible that the operation is not completed without errors. During this process, the operating system usually stops responding, so a problematic hard disk may cause complete system instability. Value=2. 53, Threshold=6. Fortunately, on this disk, there are no such bad sectors. We can discuss about improperly selected threshold values also. Some hard disk manufacturers may define 6. It is really interesting - because manufacturers usually define the designed lifetime in 5 years in product manuals. Moreover, S. M. A. R. T. How much time we would need to reach the end of the vendor specific lifetime? Moreover, the threshold value is 0 for many critical attributes. Because the Value cannot be decreased below 0, these attributes will never indicate any sign of failure - even if they . So S. M. A. R. T. It means that hard disk monitoring applications and the BIOS S. M. A. R. T. The result is that most hard disks look much better than their real status. Hard disk manufacturers may choose thresholds or algorithms to show their hard disks better than an other hard disk from an other manufacturer also. This may mislead applications and users as well. Software developers just use the manufacturer- dependent evaluation method and they do not do anything about detecting the real health status of the disks. Because of this, it is possible that the user use a hard disk monitoring application but the hard disk fail before showing any sign of problems or even a decrease in condition. Such applications may display 1. Weight of attributes. Different attributes affect disk health differently. Some attributes (for example, 1. A small change in this attribute may indicate a serious problem, for example bad motor or bearing - but maybe a weak power supply can cause this problem also. For such attributes, manufacturers often use a high threshold value, so they can be reached relatively easily. But because of the selection of the threshold and the f function described above in (1) inequality, some problems may be completely ignored. So users will not notice any changes of the critical attributes. An other problem is that the relationship between the attributes is often ignored. It is possible that two or more attribute values almost reach their thresholds - but failure is not predicted because no value reached the threshold level.#4 Lack of feedback. Without using a proper software which is able to read S. M. A. R. T. If the number of bad sectors increase slowly (the hard disk founds some new problematic sectors and tests them and reallocates them), the user may not notice anything, especially if only the screensaver is running. But during re- allocation procedure, the operating system seems to be frozen (not responding) and users may reset or power off the computer at this time. Such power loss does not help the hard disk too much in the recovery process (it will be re- started at a later time).#5 Temperature, sensor problems. Without using software, the user may not notice high hard disk temperature also. Both CPU and newer VGA cards have protection (emergency shutdown) against high temperatures but hard disks have no such protection. Even worse, hard disks are much more sensitive to high temperatures than any other component inside the computer case. That's why most manufacturers limit the maximum operating temperature in 5. Celsius degrees. Most BIOSes have support to examine the power supply voltage, fan speeds, CPU temperature etc. The BIOS S. M. A. R. T. So it is possible that the hard disk is operating in a very hot environment. But it is important to know that many hard disk temperature sensors are not too accurate (sometimes the difference between detected and real temperature can be 8- 1. Celsius degrees or even more). It is recommended to use an external device (for example an infrared thermometer) to measure the hard disk temperature and configure the difference between the measured and displayed values (calibration). So the software then displays the correct (adjusted) temperature value (if this feature is supported). It is also recommended to examine the temperature when the hard disk is idle and when it is operating for a longer time. If the temperature is too high or too low (compared to the environment) when powering the computer, it is recommended to verify the accuracy of the temperature sensor#6 Incorrect drivers. We may find many incorrect drivers for hard disk controllers. By using such drivers, one or more hard disks do not provide S. M. A. R. T. This is usually independent from the used software because applications generally use the same method to access hard disk and detect information about it. It is possible that two hard disk provide 1. PRIMARY MASTER hard disk). Software may filter this and display real (but partial) information but it is recommended to verify that the details are correct (for example, no hard disk serial number is displayed 2 or more times). Usually, the drivers support only a limited range of hard disk commands. That's why some features do not work in all cases (for example, acoustic management), even if the disk supports it.
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