H. Peter Anvin wrote:

Ric Wheeler wrote:

quoted

We still have the following challenges:

   (1) read-ahead often means that we will  retry every bad sector at
least twice from the file system level. The first time, the fs read
ahead request triggers a speculative read that includes the bad sector
(triggering the error handling mechanisms) right before the real
application triggers a read does the same thing.  Not sure what the
answer is here since read-ahead is obviously a huge win in the normal
case.

Probably the only sane thing to do is to remember the bad sectors and
avoid attempting reading them; that would mean marking "automatic"
versus "explicitly requested" requests to determine whether or not to
filter them against a list of discovered bad blocks.

Some disks are doing their own "read-ahead" in the form
of a background media scan. Scans are done on request or
periodically (e.g. once per day or once per week) and we
have tools that can fetch the scan results from a disk
(e.g. a list of unreadable sectors). What we don't have
is any way to feed such information to a file system
that may be impacted.

Doug Gilbert