“Utilizing High Capacity ATA-6 (>137GB) Drives in FireWire Enclosures”
by James Wiebe, CEO
WiebeTech LLC
October 21, 2002
© 2002 WiebeTech LLC.
All rights reserved.
This paper may be reproduced,
but only in its entirety, and only if credit is given to the author and linkage
provided to the WiebeTech website.
INTRODUCTION
The
purpose of this White Paper is to document the technical path which has
occurred that now allows FireWire enclosures from WiebeTech LLC to ship with
capacities higher than 137GB. The
reader will be given a very abbreviated history of FireWire, as well as
background information on the Oxford Semiconductor OXFW911 FireWire bridge
chip, used in many FireWire storage devices.
Finally, the reader will be shown what has recently happened that allows
the OXFW911 to provide support for high capacity OXFW911 drives.
FIREWIRE
AND STORAGE DEVICE ARCHITECTURE
Originally
envisioned by Apple Computer, Inc., FireWire is most commonly used for Digital
Video image transfer and for external storage.
FireWire drives are have become the preferred external storage medium
for personal computers.
Ironically,
Microsoft first provided driverless Plug and Play functionality to FireWire
drives with Windows 98SE. Eventually,
Apple provided similar driverless capability when OS 9.2 was introduced (with
FireWire capability cascading backwards to OS 9.1). Today, FireWire is plug and play under the following operating
systems: Win98SE, WinME, Win2K and
WinXP. Apple provides similar support
under OS9.1, 9.2, and OSX. FireWire
Drivers are also commonly used with earlier versions of Apple’s OS; albeit with
third party drivers.
FireWire
enclosures contain three critical components:
The drive mechanism, the FireWire bridge, and a FireWire interface chip
which connects the FireWire port to the FireWire bridge. (This third component is commonly called a
“PHY” – and is often ignored, even though it is an important component of
overall FireWire performance.) Of
concern to this paper is the FireWire bridge, because it provides the key
functionality and is the major performance arbitrator between FireWire storage
vendors.
Several different companies have competed to provide FireWire bridge devices to the marketplace. These are the devices which are contained within every FireWire hard drive enclosure, and are responsible for converting the FireWire protocol to that of the hard drive protocol. Without digging too deeply into the details of the various protocols (because there are several in operation all the time, both on the FireWire bus and communicating to the drive through the PHY), this paper will focus on the protocol and hardware used to communicate with the hard drive from the FireWire bridge chip.
One
of the companies which has provided FireWire bridge chips to the marketplace is
Oxford Semconductor of Oxford, England (see www.oxsemi.com). They have produced two different FireWire bridges which are
commonly used in FireWire storage devices.
The first of these was the OXFW900, still used in older, slower FireWire
drives, and the OXFW911, which is, in the opinion of the author, the volume
leader in the marketplace. While the
original OXFW900 was not fast enough for many applications, the OXFW911 has
proven to be a sturdy and zippy performer, compatible with most hard drives and
most operating systems. It is commonly
used for Digital Video editing. In
summary, the OXFW911 achieved market success for four reasons:
·
It is very fast. As
processors have gotten faster, the benchmarks of the OXFW911 have also edged up
as well, today producing benchmarks for sustained transfer rates of about
35MB/sec.
·
It is compatible with a wide range of drives. It is difficult to find a drive which the
OXFW911 has not been successfully interfaced to. For instance, the OXFW911 has been successfully connected by WiebeTech
to 340MB IBM MicroDrives (platter size a matchbox 1 inch) all of the way up to
180GB IBM Deskstars (platter size of 3.5 inches) – a capacity range of over 500
to 1 on rotating media hard drives currently shipping from one vendor!
·
It is compatible with a wide range of operating systems. As mentioned, it has been made to work with
the major personal computer releases.
Occasionally, software glitches have been corrected either by the OS
vendor or by firmware upgrades to the OXFW911.
·
It is easy to use.
Successful operation is achieved by attaching a 911 to a PHY and a hard
drive and applying power. (Important
nuances, such as PHY selection and Firmware make differences in performance.)
While
the first and last bullet are inherent in the design of the part, the middle
two bullets are a direct result of Oxford’s decision to use an embedded
reprogrammable ARM processor within the part.
As a result, Oxford and third parties are capable of doing amazing
things with OXFW911 FireWire bridges.
Whenever an operating system glitch occurred, firmware could be
manipulated to solve the problem. As a
result, the OXFW911 has not been obsoleted and clearly has a long future still
ahead of it.
A
HINT OF A PROBLEM
Desktop
drives, also commonly called 3.5 inch or IDE drives, communicate with their
host through an interface protocol. The
protocol most readily in use is the ATA-5 specification, which allows for
attachment of drives with capacities to 137GB to a computer system. The addressing limitation occurs because of
a limitation on the number of active addressing lines.
Various
hard drive vendors and computer system manufacturers could easily see that the
limit would easily be broken by advancing storage technologies. As a result, a new specification with support
of up to 144 Petabytes was adopted by the industry. An excellent resource for understanding these limitations is
provided by Maxtor at the following address:
http://www.maxtor.com/en/documentation/white_papers/big_drives_white_papers.pdf
On
October 29, 2001, Maxtor Corporation introduced a new series of drives which
had capacities up to 160GB, thus breaking the 137GB barrier established in the
ATA-5 interface with a commercially shipping mass market product. Maxtor’s new drive was compatible with the
next generation ATA-6 protocol. It
appeared that Maxtor’s new drive would not be compatible with FireWire bridge
devices designed to support only ATA-5 devices, such as the Oxford OXFW911.
For
a copy of Maxtor’s press release, see:
also
see: www.maxtor.com/BigDrive
The
OXFW911 was designed to support ATA-5 (but not ATA-6) devices, which, by
definition, are less than 137GB in capacity.
Maxtor cleverly solved their own problem when they introduced a FireWire
drive with support for their own 160GB drive mechanism.
This
FireWire drive appears to solve the ATA-5 / ATA-6 protocol problem by communicating
with the drive through a backdoor hack designed into the drive, not through a
rigorous implementation of ATA-6 control.
(The author believes these comments to be correct, but they must be
considered conjecture.) In other words,
the FireWire bridge inside Maxtor’s own FireWire enclosure was probably not
ATA-6 compatible, but it could be made to work with their drive through a
hidden protocol. The ATA-6 problem
became (temporarily) irrelevant.
Other
companies were also successful in writing a firmware hack for the Maxtor 160GB
drive using the ARM processor which is embedded in the OXFW911. It is
important to understand that this was not ATA-6 support at all, although there
was an impression that this might have been. These hacks are the basis of
all use of the Maxtor 160GB drive in conjunction with OXFW911 based FireWire
storage devices.
Other
than Maxtor, no other drives have been released with capacities greater than
137GB in the last year.
RECENT
HISTORY, BIGGER PROBLEMS
A
few weeks ago, Western Digital started shipping drives with
capacities of 180 and 200GB, and it became obvious that OXFW911's didn't work
(especially with the 200GB version). These new drives were true ATA-6
devices, and the OXFW911 did not 'speak' true ATA-6 protocol.
There
was no backdoor hack to be found. For
the first time, the OXFW911 had hit a brick wall.
Even
more recently, IBM started shipping 180GB drives that did not work with the
OXFW911. Sadly, the operating system would see all such drives as having
lobotomized capacities of 128GB.
Finally, Maxtor has come full
circle and announced even higher capacity drives which are ATA-6 compatible.
Would
the OXFW911 be able to meet this challenge? This is one feature that has
set the OXFW911 apart from competition: everytime a new drive or
OS came out, the OXFW911 ably rose to the challenge. Solutions always made it to the marketplace
via OS changes or Firmware changes.
However,
this time the OXFW911 had finally come up against a limitation that couldn't
be met in firmware: true ATA-6 support required firmware changes and
physical design changes to the FireWire bridge board.
A
RESOLUTION AND CONCLUSION
The
situation today is that OXFW911 based solutions are now shipping with ATA-6
support. In order to guarantee
compatibility with all ATA-6 devices, new firmware and new circuitry are
shipping to the marketplace. These new
products work extremely well and ably provide the ability to create FireWire
drives with ultra large capacities.
200GB units are shipping now from WiebeTech, and other vendors of
FireWire enclosures are certain to follow.
There
are implications to the consumer which are immediately obvious: most OXFW911
designs currently shipping are not capable of providing ATA-6 support (unless
the vendor specifically provides and supports an upgrade program). Products currently sitting on retail shelves
are certainly not capable of accepting all of the new ATA-6 drives. Users who are not careful in their product
and vendor selection run the risk of purchasing products that will not meet
their needs in the long run.
The
OXFW911, when modified with ATA-6 support, remains the preferred solution for
FireWire drives. It is a market leader
because it is compatible with all major operating systems and drives. It is very fast, and very easy to use. From the user’s point of view, it provides
plug and play external storage solutions.
The
recent introduction of high capacity ATA-6 drives into the marketplace briefly confounded
the OXFW911, but this has now been resolved through a redesign of the external
circuitry and by firmware update.
WiebeTech
is now shipping FireWire storage solutions which incorporate these improvements
into the product line. WiebeTech is also
supporting an upgrade program for most of its products. These upgrades allow the consumer to pay a
modest fee and receive back a FireWire enclosure with ATA-6 support. Note: The Upgrade program was discontinued on Dec. 31, 2002