Locked in cache question -Reply

Brent Skinner skinner at kodak.com
Thu May 8 04:55:58 PDT 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* skinner at kodak.com (Brent Skinner)
*
Well, the way my rather twisted mind perceives this command, the host
that locks this data into the cache doesn't want it to change. That's
why I thought that an error was more appropriate in the event that the
data was to be overwritten in some manner. Perhaps I have a distorted
view of the command's purpose.

If I continue in my perception, then I can agree with the sense key of 5, 
but an appropriate ASC/ASCQ escapes me.

If the command is just meant to keep a "hole" in cache for a particular
number of LBAs, then I'll have to implement it differently. The spec
says that only those blocks already existing in cache are locked, so
would that make the effective "hole" smaller? Would I have to retain the
knowledge of the range of LBAs the host originally requested and lock
and new data read within this range automatically in the future?

> From: PAT LaVarre <LAVARRE at iomega.com>
> I don't know enough about this subject to
> comment intelligently ... but the subject
> interests me enough that I'll comment
> anyhow.
> 
> Why report an error?  Why not just cope?
> 
> Read the block off the media into a
> temporary buffer, tagged with a nonexistent
> LBA if need be, transfer it across the bus,
> and then toss it into the bit bucket?
> 
> Me, if I were choosing a sense key, I'd
> choose "5" as in unsupported opcode.  It's
> not that it's impossible for you to do what
> the host asked - it's just that you'd rather
> not?
> 
> Come to think of it, why not just read a
> fresh copy off the media into the locked
> area of the buffer?  Does locking mean the
> data is never lost ... or does it merely
> mean that a spot in the buffer is reserved
> to hold whatever data you have in
> association with a given LBA?
> 
> Pat LaVarre
> p.lavarre at ieee.org
> 
> *
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> 


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