Andrew Morton <akpm@zip.com.au> writes:

> Andre Hedrick wrote:
> > 
> > Would it be great if Linux did not have such a lame design to handle the
> > these problems?  Just imaging if we had a properly formed
> > FS/BLOCK/MAIN-LOOP/LOW_LEVEL model; whereas, an error of this nature in a
> > write to media failure could be passed back up the pathway to the FS and
> > request the FS to re-issue the storing of data to a new location.
> > 
> > To bad the global design lacks this ablitity and I suspect that nobody
> > gives a damn, or even worse ever thought of this idea.
> 
> For the filesystems with which I am familiar, this feature would
> be quite difficult to implement.  Quite difficult indeed.  And given
> that it only provides recovery for write errors, its value seems
> questionable.

...

> What percentage of disk errors occur on writes, as opposed to reads?
> If errors-on-writes preponderate then maybe you're on to something.
> But I don't think they do?

One case were write errors are probably much more common than read
errors is packet writing on CDRW media. CDRW disks can only do a
limited number of writes to a given sector, and being able to remap
sectors on write errors can greatly increase the time a CDRW disk
remains usable.

The UDF filesystem has some code for bad block relocation
(udf_relocate_blocks) and the packet writing block "device" (it's a
layered device driver, somewhat like the loop device) has hooks for
requesting block relocation on I/O errors. This code is not working
yet though, and it seems quite complicated to get the relocation to
work properly when the file system is operating in asynchronous mode.

-- 
Peter Österlund             petero2@telia.com
Sköndalsvägen 35            http://w1.894.telia.com/~u89404340
S-128 66 Sköndal            +46 8 942647
Sweden
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