On Mon, 29 Nov 2004, Sara Fonseca wrote:
> Hi,
>
> how is the address mapping usually done in a block device?
Normally the physical and logical block numbers are the same.
> (since all
> SCSI commands see are logical blocks, the physical address that
> actually stores the logical block information shouldnt be always the
> same, should be dynamic (so you don't keep writing some physical
> blocks more frequently than others)).
That is wrong. There are only a few reasons why physical block numbers
might be different from logical block numbers. The two most common are:
So that the drive can store private data, not accessible by
logical block commands.
So that if a medium error develops in some physical block, the
corresponding logical block can be remapped to a different
address.
Yes, it is true that this means some physical blocks are written more
frequently than others. Disk drives seem to work okay, regardless.
Alan Stern
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