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Reallokierte Sektoren
In brief
Reallocated sectors are storage areas of a hard drive that the drive controller has taken out of operation because of read or write errors and replaced with spare sectors. The original sectors are no longer reachable for the operating system but may still contain old data. They must therefore be taken into account during data erasure, otherwise data remnants remain.
How reallocated sectors arise
Every hard drive has a reserve of sectors. If the controller detects that a sector no longer works reliably, it permanently redirects all accesses to this address to a spare sector. This happens unnoticed in the background. The number of remapped sectors is shown by the S.M.A.R.T. value "Reallocated Sectors Count" (attribute 5). If it rises, that is a warning sign of an imminent failure.
| Situation | Consequence for erasure |
|---|---|
| Few reallocated sectors, drive works stably | Erasure possible with software that detects remapped areas, or via firmware command |
| Many or rapidly rising number | Erasure may abort, result uncertain |
| Sectors no longer readable or writable | No complete erasure possible, destruction recommended |
Why this matters for data protection
A normal Overwriting via the operating system does not reach reallocated sectors. They can hold fragments of old files that can be read with special tools. The same applies to other hidden areas such as the Host Protected Area. More on this in the guide Securely erasing hard drives and SSDs.
At Second IT, the Blancco erasure software detects hidden areas such as HPA and DCO as well as remapped sectors, displays them and erases them. Drives that cannot be erased completely are destroyed in-house in accordance with DIN 66399 (up to H-5 and E-5).
Frequently asked questions about reallocated sectors
Is a hard drive with reallocated sectors defective?
Not necessarily. A few are normal. If the number rises, you should replace the drive and erase it securely or destroy it.
Are there reallocated sectors on SSDs too?
SSDs also replace faulty memory blocks with reserve blocks. The principle is similar; the controller handles the management together with wear leveling.
How do I see the number of reallocated sectors?
With a program that reads out the drive's S.M.A.R.T. values. The relevant attribute is "Reallocated Sectors Count".
Why does normal overwriting not reach reallocated sectors?
The controller permanently redirects all accesses to a replaced address to a spare sector. Overwriting via the operating system therefore only hits the replacement. The old sectors can hold fragments of files that can be read with special tools.
What to do if a drive cannot be erased because of defective sectors?
Then no complete erasure is possible and destruction is recommended. If sectors are no longer readable or writable, erasure can abort or its result can be uncertain. You should have the result documented.
Hidden areas erased too – with a certificate for each hard drive.
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