[ILUG] Re: When is SATA SAS?, was ITX advice

[paul at clubi.ie]

On Tue, 11 Sep 2007, Michael Watterson wrote:

> true... but I'm not convinced a *basic* SATA -IDE convvertor is any 
> more than a serial / parallel bridge. I'm sure there are fancier 
> ones.

Given that IDE and SATA are fundamentally different electrically, and 
reasonably different logically, your conviction is misplaced.

>> It doesn't affect how the controller talks to the drive.

> That's not how I understand it. You do need a SATA driver for a basic SATA 
> port. An IDE driver won't work.

My direct experience is that you're wrong.

> 1.5Gbps SATA is same speed as (P)ATA / E-IDE 133MHz interface. 
> It's only later faster revisions that are faster

- CRC of protocol+data (PATA UDMA only CRCs data, not protocol. Older
   IDEs don't CRC anything at all, IIRC).

- Hot swap

- Tagged commands and independent operation of each device..

> Unless the Mobo/Controller, Driver and Drive all support AHCI, it's 
> just IDE.

This is waffle.

It's SATA. The SATA controller just emulates same interface as 
ancient PIIX for driver software compatibility.

> Unless the drive and controller *BOTH* support SAS, it's just AHCI 
> SATA, not SCSI.

The SAS controllers I know of don't implement AHCI. But yes, you need 
a SAS host and drive.

AFAIK, SAS drives don't work with SATA hosts.

> So I think we have possibly 3 different products/ protocols that can use the 
> same physical serial cable.

Sigh, no. Last time:

SATA and/or SAS *NEVER* use anything that resembles IDE (other than 
that the SATA command set draws heavily from the IDE ATA command set, 
but then ATAPI draws from SCSI..).

AHCI is pretty common btw.

Anyway...

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
This is a country where people are free to practice their religion,
regardless of race, creed, color, obesity, or number of dangling keys...