SBC-3 r35j 4.15 text 'xxx medium operation that is not part of an xxx operation' leaves too much to the imagination

Elliott, Robert (Server Storage) Elliott at hp.com
Mon Sep 30 08:40:34 PDT 2013


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1309302_f.htm">HTML-formatted message</a>

From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Ralph Weber
Sent: Friday, 27 September, 2013 4:17 PM
To: t10 at t10.org
Subject: SBC-3 r35j 4.15 text 'xxx medium operation that is not part of an
xxx operation' leaves too much to the imagination
While some of those present thought the intent was somehow related to
specifying the proper operation of cache coherency implementations, Western
Digital reviewers found the following two list introductions incomprehensibly
vague in SBC-3 r35j.
  *   For each LBA accessed by a write medium operation that is not part of a
write operation:
  *   For each LBA accessed by a read medium operation that is not part of a
read operation:
Is this intended to reach into the design of background operations?
Proposing a solution based on the current, quicksand text seems like a
dubious endeavor, at best.
If the intent is to specify who a device server maintains cache coherency,
the majority of Western Digital reviewers question the need for such
untestable requirements in a T10 standard. If some other concern underlies
the existing text, then perhaps the addition of an e.g. immediately prior to
the colon will set the proper tone.
The intent is to be clear that every read medium operation must get data from
the cache if more recent data is there, and every write medium operation must
keep the cache up to date.
It's a catch-all for commands like WRITE AND VERIFY and other model material
that refers directly to medium operations but doesn't mention the cache
impacts:
		Page 195
The WRITE AND VERIFY (10) command (see table 111) requests that the device
server:
1) transfer the specified the logical block data for the command from the
Data-Out Buffer;
2) perform write medium operations to the specified LBAs;
3) perform verify operations from the specified LBAs; and
4) if specified, perform a compare operation on:
		A) the logical block data transferred from the Data-Out
Buffer; and
		B) the logical block data from the verify operations....
Maybe WRITE AND VERIFY should just be described as performing a write
operation, because the verify operation includes the write medium operation
if needed.
One fear is clear. If nothing is done, over jealous test engineers are likely
to extend their vision of the cache to include the sector write buffer that
is part of the hardware that actually records data on the medium.
Warning: This comment is the result of a very preliminary review by Western
Digital engineers. The Western Digital review of SBC-3 r35j is ongoing, and
more issues seem likely to be unearthed. Due to the gravity of this issue
Western Digital concluded that prompt disclosure would best serve the
interests of T10 and the industry.
All the best,
.Ralph



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