[KLUG Hardware] SerialATA blurs the RAID landscape even more -- WAS: SCSI card recommendation

[Bryan J. Smith]

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On Tue, 2002-11-05 at 11:13, Bryan J. Smith wrote:
> SerialATA improves many things by finally removing that
> _stupid_ "slave" option (which I _never_ use).

SerialATA really does a lot to improve ATA.  ATA (AT Attachment) was
designed as an extension and standardization of the existing IDE bus,
which itself was an evolution of the previous ESDI technology.

SerialATA offers ...

1.  Direct point-to-point (host-to-device) DMA transfer

Although you can get somewhat of the same by using only one drive per
[parallel] ATA channel, SerialATA is optimized for point-to-point.  This
is ideal for intelligent RAID controllers too, since devices don't share
a bus.

[ Furthermore, 2 SerialATA "ports" can "fool" legacy configuration
systems (BIOS, OS, etc...) as looking like a master/slave, even though
they don't.  Hence why new southbridge chips have 2 SerialATA "ports"
and 1 ATA channel.  But it doesn't act like a "master/slave" though.=20
SerialATA can also use existing ATA controller logic, by adding an
external PHY chip, although it doesn't give SerialATA quite all its
advantages over parallel ATA. ]

2.  Low data pin count, allows direct, multi-port controllers

A follow-up to #1, another advantage for intelligent RAID, 7-pins per
port mean controllers can have multiple, direct lines to multiple
SerialATA ports.  This is why SerialSCSI is being introduced as well,
because of the huge advantage over parallel data transfers.=20
Point-to-point is better for controllers, especially if the controller
can talk directly to multiple devices simultaneously, instead of each
"bus" sharing the same "bus" to the controller.

3.  Fixed location, single edge connector with hot-plug capability

SerialATA uses a 7 staggered-pin data connector in a fixed location with
an, optional, 15 staggered-pin power connector in a fixed location.=20
While many early SerialATA devices will ship with a legacy Molex power
connector, often in place of the standard 15-pin power connector, the
latter will eventually be sported on all SerialATA devices.  The
staggered-pin arrangement lets the firmware detect if the device has
been plugged or plugged, allowing hot-plug -- including handling safe
power transient changes as standard.

--=20
Bryan J. Smith, E.I.            Contact Info:  http://thebs.org
A+/i-Net+/Linux+/Network+/Server+ CCNA CIWA CNA SCSA/SCWSE/SCNA
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