[dm-devel] Error target causes entire device to error

[Phillip Susi]

Milan Broz wrote:
> it seems that someone optimize the request, direct io does what you want.
> in fact, dm receives bio requesting 1024 bytes, not 512.
> (optimizing it to page size, but here it is limited by device size).
> 
> assuming that your arch has 4kb pages, try to setup device with
> 0 8 zero
> 8 8 error

Ahh, of course!  The buffer cache is trying to read a whole page.  And I 
guess it just gives up and fails the entire request rather than retrying 
only on the requested area.