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Bad sectors (disk read errors) and what to do
about it
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Summary:
disks can develop bad sectors over time.
Background information.
DiskPatch allows disk cloning and disk surface scanning (detect
and fix bad sectors).
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Keywords:
read error, bad sector, sector reallocation, disk cloning,
S.M.A.R.T.
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Created: 28-11-2006
Last edited: 20-01-2010
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| Disk Read Errors |
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Data can be lost due to unreadable or 'bad' sectors. If a file
occupies a sector that returns an error on read, the file may become
unusable.
If the MBR or a sector that contains a partition table or boot sector
can not be read, an entire disk or drive may become inaccessible! Bad
sectors in a system area are a recipe for disaster.
There are 2 ways of dealing with data loss due to read errors:
1. Clone the disk to a "known to be good" disk
2. Repair bad sectors in-place
If you have reason to believe a disk's condition is rapidly deteriorating,
always clone the disk!
If a partition was lost because the partition table sector could
not be read, apart from repairing the bad sector you will also need
to rebuild the information that was in that sector.
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| Cloning a bad
or corrupt hard disk |
As mentioned, if there's any sign a disk's health is rapidly
decreasing you should first clone the disk, and then worry about
the rest.
To be able to clone a disk with read errors or logical corruption
you will need a data recovery utility that is designed to cope with
this type of error. The tool of choice must gracefully handle read
errors and get as much data from the source disk as possible. It
should ignore any (corrupt) logical structures on the disk.
It is preferred the utility runs outside of Windows and that it
logs all read/write errors to a file. |
| Repairing corrupt or bad
sectors |
If a sector's data is corrupt, it can often be
reconstructed using ECC error correction. If the sector is too
unreliable to store data again, it will be reallocated; the
sector is taken out of service and replaced by one from the
'spare pool'. The spare pool is a group or multiple groups of
spare sectors available on any modern hard disk.
You can
detect unreliable sectors by scanning your disk's surface
with DiskPatch. You can check the state of the disk by running
a disk health check (S.M.A.R.T. check).
If the data from a sector can not be read even after error
correction, it becomes pending for reallocation; it is not yet
automatically swapped.
On write an error-producing sector is reallocated if any of the 2 following
events occur:
- a sector can not be written to, or
- the
sector written to is pending reallocation. |
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