A step-by-step example of how to use this function can be found here.

Introduction

DiskPatch allows you to scan a selected partition, an entire disk or a user defined area of the disk for what is commonly referred to as 'bad sectors'. Bad sectors can be the cause for many types of data loss: files may become corrupt because some of the sectors that the file was saved to have become unreadable, or whole partitions may become in-accessible because the structures that define the partitions contain unreadable sectors.

Sometimes disk problems can be fixed by the tools that are included with several operating systems: scandisk, checkdisk or similar tools will sometimes restore access to files if disk structures such as the FAT were damaged. These tools however do not correctly address the problems that might arise from bad sectors. Let's look at this a bit more closely:

The first priority for a tool such as scandisk or checkdisk is a consistent file system. In other words, their main job is to keep the file system okay, not the actual data that resides on the disk. If a problem occurs with the file system, scandisk or checkdisk may repair the damage, but always in favor of the file system. The result may be that access to actual data can be compromised because the repair could only be completed by removing references to certain files from the file system. These removed files (or fragments of them) then appear as filexxxx.chk files (in case of scandisk or checkdisk).
Another point of interest is how tools like scandisk and checkdisk handle read problems. To put it simple: they don't do that very well. If they encounter a read problem (a bad sector) the entire cluster that the bad sector was a part of, is discarded. If a disk has large clusters (32K clusters for FAT32 is normal, that's 64 sectors per cluster) you lose capacity, not to mention the impact this may have on files or file system structures. Also, since scandisk and checkdisk by default only check the used areas of the disk, bad sectors may not announce themselves until data is written to one. That may be too late.

DiskPatch surface scanning

DiskPatch will scan each sector on the disk, whether it's a part of a FAT, filled with data or empty. By allowing DiskPatch to detect 'bad sectors' before the Operating System or the on-board disk repair tools do, you allow your hard disk's internal error management to take care of the bad sector: it will be re-allocated.

The surface scan is a smart scan: the scan starts by reading sectors along the disk. Once a read error comes up the bad sector will be re-read and written to as needed, to try to read the data and 'repair' the bad sector. The sector will be verified and then the scan will continue.
By default DiskPatch will stop the scan after the first read error was found. This way you are made aware of the state of the disk before actual repair attempts are made. This behavior can be changed by changing this setting in the settings screen before starting the surface scan.

DiskPatch interacts with sectors on a low level and does not interact with the file system. When DiskPatch detects a read problem, it is handled (by the disk) using one of the following strategies:

• Error on read that can be corrected:
  Hard disks apply multiple strategies for correcting 'bad' data allowing the disk to provide you with your data even if a sector could not be read entirely. If the data in a sector can be recovered using this strategy, the data is copied to a spare sector and the bad sector is taken out of service.
• Error on read that could not be corrected:
  If a sector can not be read and the hard disk's automatic error correction can not recover the data in the sector, the sector will become a candidate for reallocation. A read error will be reported. The candidate for reallocation will be reallocated when the sector is accessed for a write operation.
• Error on write:
  The bad sector is taken out of service and the data is immediately written to a spare sector. In other words, the bad sector is 'reallocated'. If sectors were corrected they will not appear again during the next disk surface scan; this means that if errors that appeared in the first surface scan do not appear in the next surface scan, these 'bad sectors' were reallocated and should now be available again for use.

Using DiskPatch to find and correct disk errors

There are a number of configuration settings that affect DiskPatch's behavior during surface scanning. Make sure these settings are correct before starting the scan.
The settings that affect surface scanning are:

• read retries
• write retries
• read error threshold
• write error threshold
• interrupt scan on first read error
• disk reset after error
• write sector after read error
• verify fixed bad sectors

If a read error is encountered and the data can be read from the sector, the data will be placed in a spare sector and the problem is solved.
If the data can not be read, a read error is reported and the sector becomes a candidate for reallocation; the data in the sector is lost and the candidate sector will be reallocated during the next write operation. What happens next depends on the configuration settings. By default DiskPatch will attempt to write to the sector to enforce the reallocation (the 'write sector after read error' setting). That will be followed by another read attempt to verify that the sector has indeed been reallocated (the 'verify fixed bad sector' setting). If that last action fails the sector is reported as bad by DiskPatch, and will still be considered bad by the disk.

You can use our S.M.A.R.T. utility or the disk's manufacturer diagnostic tool (refer to the disk manufacturer website) to determine the exact condition of the hard disk. Once the pool of spare sectors has been exhausted bad sectors can no longer be reallocated, and bad sectors will continue to appear during surface scans.

Settings that affect a surface scan:

• interrupt scan on first read error:
  on by default. When a read error is encountered DiskPatch will halt the surface scan and display the settings screen. Adjust the settings as needed and continue the scan by exiting the settings screen (press <esc>). By doing this the user is made aware of the state of the disk. If you wish to let the scan run uninterrupted, adjust this setting in the settings screen before starting the surface scan.
• disk reset after error:
  when enabled DiskPatch will send a disk reset command to the hard disk after encountering a read- or write error. This may have a positive effect on further read or write actions, but might also slow down the read- or write operation considerably.

To run a surface scan:

Select [Disk related tasks], [Surface Scan], then select a partition to scan or select a region of the disk manually:

To scan the entire disk, select 'entire disk' and leave the suggested default values (just press <enter>).

When you press <esc> during the scan, DiskPatch will display the settings screen:

You can adjust settings that affect the surface scan, or abort the operation by selecting the 'Abort' option. Press <esc> again to exit the settings screen and continue with the new settings.