Mike Accetta wrote:

is at the mercy of the low level disk driver.  We've observed abysmal
RAID1 recovery times on failing SATA disks because all the time is
being spent in the driver retrying operations which will never succeed.
Also, read errors don't tend to fail the array so when the bad disk is
again accessed for some subsequent read the whole hopeless retry process
begins anew.

This is one issue I believe the Western Digital RE/RE2 drives address. 
The "TLER (time-limited error recovery)" feature limits retrys to try to 
prevent this. I have the figure of 5 seconds in my head, but could be wrong.

Not sure if the Seagate nearline range offers the same sort of thing.

Regards,

Richard