How it is possible that the health of the hard disk is low, the text description shows the bad sectors but the tests do not show any problems?
When the hard disk finds a bad sector, it tries to save (reallocate) the contents from the sector to the spare area. When this completes, the original sector location is marked and disk does not use it any longer: all further read and write operations are redirected to the spare sector. This way the tests (which does not only mean tests of this software) can only access this modified surface. In an optimal situation the surface is really perfect - the problems are fixed, bad areas are no longer used. Problem can be caused only if the bad area is relatively large (thus the health is low) and more and more problems (for example weak and bad sectors) born. To fix these issues, it is receommended to use the tests built into Hard Disk Sentinel because they can verify and fix the problems under a controlled environment. For more information about problems, please check the text description section.
All tests are designed to reveal disk problems. The health is calculated based on the problems found with the hard disk, the test may cause decrease of health. The health could increase only if the problems would become "hidden" (but not fixed!). This is not possible - except if the drive had weak sectors before the test and their count can decrease (even back to zero). The count of other problems detected (and fixed) by the hard disk cannot be decreased and would not be good, but by using the "offset" column on the S.M.A.R.T. page these problems can be ignored if the drive status is stable. For more information, please check the text description and the temperature calibration sections.
Why does the test find more or less bad sectors than displayed in the text description?
The bad sectors appear in the text description are already reallocated by the hard disk, which are no longer used. The bad sectors revealed by the test are still on active surface so these can potentially cause data loss. Our goal is to force the hard disk to reallocate these sectors also to prevent their future use. Usually the disk works better (even its health value may decrease because of the reallocation).
Can the health be improved? Can it be restored to 100 % ?
If the hard disk had weak sectors, their status can be improved during the tests. This may result in increased health value - even to 100 % if there were no other problems found with the drive. In all other cases, the health may decrease if the status of the drive is not stable and newer problems are revealed.
If the drive is stable: the health does not change even after many passes of the write tests, the previous problems may be cleared on the S.M.A.R.T. page by using the Offset column. This way the health can restored to 100 %.
Warranty replacement is possible only at 0 % health. If the health is higher (but still low) it is recommended to start the tests (even many times) to reveal further, currently not detected problems.
Why it is good to use the disk tests of Hard Disk Sentinel? Why it is not enough to simply copy files (to force reallocation)?
During the tests in the software, the hard disks are under better control and monitoring compared to plain file operations. The file system is unmounted to prevent the operating system and other software from accessing the disk and the status of the file system (for example fragmentation) does not affect the test. The performance of the blocks, retry count and disk health and tempearature are all factors which are continuously monitored during the tests. It is even possible to inspect the sector contents any time. Like surgery is only possible in hospital - hard disk testing and repair has its own controlled environment.
Generally, two different tests are available: hardware self test, and software testing (both are available in Hard Disk Sentinel). The later category contains the random seek time test also, which is a special test as it does not verifies the surface, just the seek capabilities of the drive.
The hardware tests can be better than software methods because they can examine the disk system and components (for example head, servo, electric components and so) by a special way which is not possible by software methods. It does not affect the stored information so they can be used any time (on IDE and S-ATA hard disks which support them), without any special preparation or backup. The use of hardware tests are recommended periodically, especially on perfect (or near perfect) disks to reveal any hidden problems.
In some cases, these hardware tests (Disk -> Short self test, Disk -> Extended self test) are not available, not supported or they result in an error quickly even in relatively low number of problems. No further information is returned about the result, for example it is not possible to list the sector(s) which are damaged. In such case, an appropriate software testing method is required.
When we speak about software testing, it is important to know that the WRITE operation affecting the disk surface is the most important: this forces the hard disk to verify the integrity of the data sector, reallocate it if required and repair weak sector. Because of this, all READ type tests (for example, scandisk but the format also) cannot be used to repair disk problems (and in many cases they even can't detect such problems). Scandisk verifies and fixes logical errors only (file system related errors) which are not really connected to physical disk status, errors (this is why they usually vanish after complete re-partition and re-format of the disk).
The WRITE tests are usually destructive as they need to overWRITE the stored data. In all cases be very careful before starting any of such disk tests, it is important to backup all data!
The software tests are recommended to use less frequently compared to hardware tests. Software tests are useful when
In such cases, it is recommended to use the read test first which does not affect stored information. The read test cannot fix any errors but can show which areas of the drive are not perfect, damaged and/or slowly accessible and shows the temperature and performance characteristics of the drive. The real verify and fix of errors is possible later by a suitable write test. In case of more problems, it is recommended to backup the data and use the reinitialise disk surface test (even with a level 3 or higher). Other software may (incorrectly) call a simpler version of this test as low level format.
IMPORTANT: The developer offers no warranty on the stored data on any disks! Under all circumstances it is recommended to backup ALL DATA and read the description for the tests carefully before starting any of the tests.