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Hale,
The 'right thing' for the disk drive behavior that I was
referring to is the assumption that after a write to the disk, any read
from the same address any time after the write, will produce the same
data. The presence or absence of a cache should not affect disk
read/write behavior. I don't think we need a standard, a spec or a
white paper for people to understand this.
Drive manufacturer are free to implements something that doesn't
behave this way, but they will have a hard time getting a logo. We
haven't had a hard drive fail for a long time and that is why I say they
have done the right thing for years.
FUA is not new to drive manufacturers. The proposal to add FUA
to T13 was made a year ago. The only issue that a hard drive
manufacturer has had was around releasing which has started this whole
thread. That issue was very quickly resolved. Interestingly, very
little noise about FUA has come from the hard drive manufacturers,
however, if you think that FUA as it is in the spec, I suggest you do
what Western Digital did and write a proposal to change it.
Nathan
-----Original Message-----
From: Hale Landis [mailto:[EMAIL PROTECTED]
Sent: Friday, June 27, 2003 8:58 PM
To: T13 List Server
Cc: Nathan Obr
Subject: RE: [t13] Re: hmmm.. no comments?
On Fri, 27 Jun 2003 13:44:26 -0700, Nathan Obr wrote:
>I do assume that drive manufacturers will do the right thing, but that
>is only because they have for years.
Are you sure? What is the definition of "right thing"? Is it some
test Microsoft uses for logo certification? Is it just some feeling
that everyone is doing the "right thing" so there is no problem? I
don't understand why you seem to have no concerns about this.
>The only requirement that a host
>has on a device with a cache is that the cache doesn't change the
>behavior of the device.
What behavior? Where is that defined? Is there some standard for how
a disk drive is supposed to work? Is there a standard for how a disk
drive cache should work? If such standards exist I've never seen T13
or ATA/ATAPI-x reference them. Does Microsoft have a document that
describes in detail how a disk drive works and/or how a disk drive
cache works? If so, can you share it with us?
>Any caching scheme that returns data for a
>sector other than the last data written to that sector has a design
>mistake,
Huh? It would not be a "design mistake" if the manufacturer product
specification defined that their drive did not operate in that
manner. And I can think of design reasons to implement a drive in a
manner that you would call a mistake. Sure that may not be a "good
design" but there is no standard that would say it was
invalid/illegal. If you or Microsoft think such implementations are
not possible and/or would never happen then I think you and Microsoft
need to learn more about how disk drives are operate and how they are
designed.
>however, I don't believe any caching algorithm is considered
>"valid" to ATA/ATAPI as I am not aware that ATA comprehends caching.
Hmmm... ATA/ATAPI-x define SET FEATURES commands to turn read/write
caching on/off and then there are the FLUSH CACHE commands. Maybe
ATA/ATAPI doesn't define how read/write cache should operate but
ATA/ATAPI does allow the host some control of this drive activity.
>I believe that device caching behavior is outside of the scope of the
>ATA protocol and off topic for this forum.
Perhaps, but again that just reinforces the need for an answer to my
questions above, especially the question of where is the
specification or standard or Microsoft document that defines how a
disk drive and/or a disk drive read/write cache are implemented.
In another email to the list today you said FUA should not cause
hardware changes in a drive (I think that is what you said). Before
you assume FUA is so simple I think you need to talk to some disk
drive designers.
Hale
*** Hale Landis *** www.ata-atapi.com ***
