Re: [SLE] OT -- SAS (Serially Attached SCSI)

On 10/30/06, Greg Wallace <gregwallace@xxxxxxxxxxx> wrote:
Could one of you gurus give me a brief description of what it means to
have a SATA-SAS Integrated card in a computer? I assume this somehow allows
you to link a SATA drive to a SCSI drive in your machine, but I don't
understand what that does for you.

Thanks,
Greg Wallace

Greg,

It means the SATA//SAS controller can talk natively to either a SATA
drive or to a SAS drive. You buy the one you want and plug it in.

Details and background for the bored:

I assume your aware the TCP/IP traffic can be sent over various media
(ethernet, dsl, T-1, E-1, wireless, etc.)

That is because a layered approach is taken in a lot of communication
systems. The 7-layer model even formalizes it.

From the opposite perspective a T-1 can carry channelized voice
(traditional usage), channelized data, or unchanelized data. The data
is what can be treated as IP packets.

Now in the disk drive world previous to 1990, this was not really
true. An IDE cable was used exclusively to carry a predefined set of
disk drive commands. And the command set was hardwired into the drive
electronics.

SCSI was a little better back then in that a small embedded cpu was on
the drive to act as a command interpreter. This allowed the main CPU
to offload the work to the SCSI embedded cpu.

Things have advanced significantly since then. Now a highly layered
approach is being taken by both ATA and by SCSI.

ATA now supports PATA and SATA (Parrellel & Serial)

SCSI supports a whole host of connection types (Parrellel SCSI (in
multiple viersions), Fibre-Channel, iSCSI, USB, Firewire) and even an
IDE cable is used for ATAPI. (ATAPI uses SCSI commands across the IDE
cable)

Fortunately when ATA and SCSI decided to implement a high-speed serial
connection / media (SATA/SAS), they choose to use exactly the same
one.

Thus the cable a lot of us call a SATA cable could just as easily be
called a SAS cable.

So te designers of a disk controller that supports the new cabling
have 3 choices:
SATA only support
SAS only support
Both SATA and SAS support

Hope that helps
Greg
--
Greg Freemyer
The Norcross Group
Forensics for the 21st Century

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