In reference to hard disk drive technology SMART stands for Self-Monitoring And Reporting Technology.  SMART is a system built into modern hard drives and SSDs that is designed to constantly monitor a number of different parameters and provide an early warning system if the device is beginning to fail.


This article is designed around SMART as it relates to traditional hard disk drives, Whilst SMART is available on most SSDs, it often monitors different parameters as the underlying data storage technology is quite significantly different.  If you have reached us after looking for a data recovery service, following a hard drive failure, use these links.

SMART enabled hard drives (which include all modern IDE, SATA and SCSI devices) can communicate developing problems with the host system, either through the operating system of the computer, third party SMART monitoring tools or the computers BIOS.  Where SMART is enabled and monitored, error messages appear that advise the user of an impending failure, normally recommending that they back up their data.  Once the parameters that are actively monitored exceed certain thresholds a complete disk failure is very likely within a short period of time.

What Parameters are Monitored?

The type of hard disk problems that are monitored and indeed, the way in which they are reported can vary with drives from different manufacturers.  We won't go in to the full list of parameters within this article as those recorded, even the way in which they are recorded can vary from manufacturer to manufacturer and even between different generations of devices.

The most important attributes tend to be those related to the drive developing bad sectors.  Bad sectors are sectors of a hard disk that are unreadable, or where the error checking information that is stored at the end of the sector does not match the calculated value of the data within the usable portion of the sector.  Bad sectors can be caused by a number of issues, including:

  • Partial or complete failure of one or more of the drive's read/write head elements
  • Failed write attempts
  • Physical damage to the drive's platters where the data is stored
  • A break down of the platter media's ability to store magnetic data

The SMART parameters monitored that relate to unreadable sectors include:

Reallocated Sectors Count - when a drive encounters a read error during normal operation a number of internal processes begin.  These include attempts to read the data from the sector, ultimately resulting in it being marked as bad and added to the drive's grown defects list.  When this happens, so as not to lose capacity of the device a spare sector taken from a bank of reserve sectors designed specifically for this task is 'remapped' and used for any future read/write attempts from that particular sector.  This parameter shows the number of such sectors that have been encountered throughout the drive's lifetime and is a fairly reliable means of identifying a failing disk before it fails permanently.

Spin Retry Count - The spin retry count is a measure of the number of times that the drive has failed to reach the correct speed on power up attempts. An issue developed with the drive spinning can indicate problems with the motor losing efficiency or even partially seizing.  Spin retries can also be caused by electronic issues, often with the power supply to the motor.

Reallocation Event Count - This attribute displays the total number of attempts that the drive has made to remap bad sectors, it includes sectors that have been successfully remapped as well as those that have not.

Current Pending Sector Count - Before a sector is marked as defective and remapped it is added to the drives internal list of problem sectors.  These are sectors that the drive has had problems reading in the past but that have not yet been remapped.  The drive will attempt to remap this kind of sector the next time that it is able to write to it.

What Should I do if my Drive reports an Impending Failure?

Most SMART warning messages advise that you back up your hard drive immediately, this is good advice as, although SMART does not always predict a failure before it happens, when it does, it is a warning that failure WILL occur soon thereafter.  Whilst the drive is still in a working state it is critical that any important data be taken off and stored safely.  If this is successful the drive should then be replaced immediately.  If it is not successful a data recovery company should be contacted immediately.  Data Recovery companies can often extract all data, even in the worst cases of drive failure.

Can I monitor my drive's SMART?

There are a number of ways to monitor SMART, including free or chargeable software that works on almost any operating system, TRC Data Recovery produce a utility for Mac OS X based on an open source SMART tools.

How do I prevent this kind of failure?

There is no guaranteed way to prevent against SMART failures, the attributes that are monitored are merely a representation of certain aspects of the drive's operation.  This means that prevention is not possible, however, using a good backup policy can prevent losing data as a result of hard drive failure.

With faster broadband internet speeds becoming increasingly available, backing up all of your data to a managed cloud based backup service is a realistic and well recommended option for keeping your data secure regardless of what happens to your hard disk or its SMART monitoring system. Cloud backup, however, is a topic for another article.

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