This message is from the T13 list server.
All Maxtor SATA/PATA drives operate in an equivalent to restricted
ordered mode, whereby time-coherent data integrity is enforced and
guaranteed.
For example, given this set of queued overlaps with the oldest command
on the bottom:
r3r3r3
w2
w1w1w1w1
In that case, the data returned as part of r3 is guaranteed to look
like:
w1w2w1
We will never return 'w1w1w1' for r3 in the above circumstance, nor will
we ever return 'w0' or whatever the prior state of those blocks were
prior to the w1 command.
--eric
PS: We know the specification doesn't require this behavior, but this is
how we chose to implement queueing on our desktop products. I obviously
can't speak to what the other vendors are doing.
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Jeff Garzik
Sent: Friday, January 28, 2005 12:53 PM
To: Dennis Moore
Cc: Forum@t13.org
Subject: Re: [t13] Queuing
This message is from the T13 list server.
Dennis Moore wrote:
As I recall when overlap/queuing was proposed for ATA devices
(X3T10-95-258) that the handling of command reordering was
left to the
drive with no restrictions. It was the equivalent of SCSI
task attribute
SIMPLE and mode UNRESTRICTED. I can't find anything in current
documentation that confirms or denies that. Are drives that support
queuing today doing unrestricted reordering? Are SATA NCQ
devices going
to do unrestricted reordering? Any help is most appreciated.
In the lack of further information, one must -assume- that
the devices
are doing unrestricted reordering.
And I think it's likely, given that unrestricted ordering
gives the ATA
device the most flexibility in optimizing the outstanding ATA
commands.
Jeff
