| Bad sectors (disk read errors) and what to do
Disks can develop bad sectors over time, or by experiencing
improper handling. Diagnose a disk using S.M.A.R.T. or by running a surface scan.
Repair bad sectors in-place (if there are few) or clone a disk (if
there are many).
|Disk Read Errors
Data can be lost due to unreadable or 'bad' sectors. If a file
occupies a sector that returns an error on read, the file will become
unusable. If there are too many bad sectors you may even be unable
to access an entire volume.
If the MBR or a sector that contains a partition table or boot sector
can not be read, the entire disk or drive will 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.
|Cloning a bad
or corrupt hard disk
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.
A successful strategy to copy as much data of a disk as possible is
doing multiple passes. In a first pass try to avoid disk hangups by
not trying too hard and skip over errors. The cloning software keeps
track of the areas it skipped and processes those areas during the
next pass. DiskPatch clones disk
to disk using a 2 pass clone. iRecover
writes a raw image file that can later be processed, also using a 2
|Repairing corrupt or bad
|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.
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). iRecover also can check
a disk´s SMART status.
If the data from a sector can not be read even after error
correction, it becomes pending for reallocation; it is not yet
On write a sector is reallocated if any of the 2 following
- a sector can not be written to, or
sector written to is pending reallocation.