HDD Implementation Of RC (Read Continuous)

Tom Wicklund wicklund at intellistor.com
Fri Nov 15 15:52:37 PST 1996

* From the SCSI Reflector (scsi at symbios.com), posted by:
* wicklund at Intellistor.COM (Tom Wicklund)
Tom Gardner writes:

 >      Has there been any discussion of the actual implementation of the Read 
 >      Continuous bit.  As an old DASD hand (that old!) I'm extremely 
 >      reluctant to ever send bad data to the host without immediately so 
 >      stating.  However the spec seems to permit it.
 >      The question is are HDD's which support RC really sending bad data or 
 >      just using the RC as a global switch to minimize the length of error 
 >      recovery.  

Traditionally (at least from markets I worked in) RC means no error
correction.  Users who turn on RC are those who don't care about a few
bits in error but care greatly about lost performance, for instance
imaging applications which store real time video.  A few bit error
might show up as a pixel or two wrong, but this isn't a big deal at 30
frames / second.  Video is less tolerant today though since
compression means that bit errors are now important.

Thomas Wicklund

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