VERIFY & how the data got into the cache
Elliott, Robert (Server Storage)
Elliott at hp.com
Mon Sep 30 08:57:04 PDT 2013
Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1309305_f.htm">HTML-formatted message</a>
The blue text is your proposed text, not the sbc3r35j text. sbc3r35j does
not specify "read cache operation" for verify; it specifies "write medium
For each LBA accessed by a read operation that is not a verify operation:
1) if a cache contains more recent logical block data for that LBA than the
medium, then the device
server shall perform a read cache operation from that LBA; or
2) the device server shall perform a read medium operation from that LBA.
For each LBA accessed by read operation that is a verify operation:
1) if a cache contains more recent logical block data for the LBA than the
medium, then the device
server shall perform a write medium operation to that LBA;
2) the device server may invalidate that LBA in the cache; and
3) the device server shall perform a verify medium operation from that LBA.
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Ralph Weber
Sent: Monday, 30 September, 2013 10:34 AM
To: t10 at t10.org
Subject: VERIFY & how the data got into the cache
Unless I misheard them, WD engineers beg to differ with the following
comments in the "4.15 specs for read operation" thread:
For each LBA accessed by a read operation that is a verify operation, the
device server shall perform a read cache operation only if:
a) the logical block data in the cache for that LBA is the result of a read
medium operation; and
b) no subsequent write operation has been processed for that LBA.
RE: It doesn't matter how the cache got the data. If there is more recent
data in the cache, all verify operations need to force that data to media
before performing the verify medium operation.
How the data got into the cache very much matters (or so my experts tell me).
For this reason, WD engineering sees the current 4.15 requirements as being
fixated on the wrong thing.
VERIFY commands are required to use data that is read from the medium. If the
cache contains data that is newer then:
1. that data must be written to the medium,
2. the cache must be invalidated, and
3. the data must be read from the medium (and stored in cache if so
Any specification that says otherwise is misleading the reader.
It is not acceptable to write the newer cache data to the medium and then use
the cache contents without first reading the medium, unless the goal of the
letter ballot changes is to negate the first sentence in the SBC-2 definition
of VERIFY ... to whit:
"The VERIFY (10) command (see table 53) requests that the device server
verify the specified logical block(s) on the medium."
Furthermore, the "newer data in cache" issue should be covered by b) in the
WD proposed wording.
All the best,
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