Dear Oribe-san,
The "Allocation Unit" is information passed FROM the host to the DRIVE, and not
from the drive to the host, as you suggest.
It is meant for a 'smart' drive that handles streaming by itself. In such a case the 'smart'
drive has to know something about how data is to be accessed by the host, specifically
in what size units it is accessed.
Relevant documents are:
d99135r7.doc/pdf A/V Model and Definitions
d99128r10.pdf Proposal for Streaming Data Transfer Feature Set
It is only relevant for drives supporting the Streaming Data Transfer Feature Set.
The Streaming Data Transfer Feature Set allows for two methods of operation:
Smart Host & Drive with Command Completion Time Limit
Configure Stream and Allocation Unit irrelevant
Dumb Host & Drive with stremaing/scheduling capability
Configure Stream and Allocation Unit necessary
Kind regards,
Stephen.
--
Dr. Stephen Cumpson, Senior Scientist,
Storage Systems & Applications, Building WY 1 45, (WY12),
Philips Research Labs., Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands
Tel.: +31 40 274 2762 Fax: +31 40 274 4648
Email: mailto:[EMAIL PROTECTED]
Web: http://www.research.philips.com/
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"Hiromichi Oribe" <[EMAIL PROTECTED]> Sent by:
12-08-2003 19:09
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To: "T13" <[EMAIL PROTECTED]> cc: (bcc: Stephen Cumpson/EHV/RESEARCH/PHILIPS) Subject: [t13] ATA/ATAPI-7 What is Allocation Unit(AU)? Classification:
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Does anyone know how to use "Allocation Unit"? I can't find anywhere in the ATA/ATAPI-7 document describing how to use this…
Is this just "useful information" for host to know?
Does AU have something to do with Command Completion Time Limit (CCTL) for streaming?
Followings are the only places I can find through out the document.
3.1.11 AU Allocation Unit: The allocation unit is the minimum number of logically contiguous sectors on the
media as used in the Streaming feature set. An Allocation Unit may be accessed with one or more
requests.
4.17.1.2 Flush to Disk bit
The Flush to Disk bit in the WRITE STREAM command specifies that all data for the specified stream shall be
flushed to the media before posting command completion. If a host requests flushes at times other than the end
of each Allocation Unit, streaming performance may be degraded. The SET FEATURES command to
enable/disable caching shall not affect caching for streaming commands.
6.8 CONFIGURE STREAM
Sector Count Current -
The size of an Allocation Unit in sectors (bits 7:0).
Sector Count Previous -
The size of an Allocation Unit in sectors (bits 15:8).
Hiromichi Oribe
[EMAIL PROTECTED]
Iomega Corporation
1821 West Iomega Way, Roy, Utah 84067
tel 801-332-5360
fax 801-332-4667
