[kwlug-disc] Multi-bay docks ... 1 at a time??? [Was: Re: Linux-compatible eSATA expansion cards]

[unsolicited]

John:

Thanks. I lost sight of that rather earlier reference to chipsets that 
Khalid picked up on / notes below. However, I suspect you picked up on 
'chipset' from my comment that most SATA controllers (or motherboards) 
don't put in PMP capabilities as they don't have to meet spec. / keep 
costs for the masses down.

Which makes me think (thank you), if one intends to run multiple sata 
drives over a single link, inherently you will have to buy a controller 
card (such capabilities not being otherwise present, as above). Assuming 
PMP is not present in the sata express spec., nor any sata spec coming 
any time soon.

But that does just lead to one of my original speculations - one would 
have expected a product containing multiple bays to have a PMP 
controller within the unit capable of multiplexing the multiple drives 
over the single sata link. That they are not required to be sold that 
way just goes back to Caveat Emptor. Sadly.

Nor would one reasonably expect to see such a controller in any laptop, 
leading me to conclude and agree with what someone said some while back 
- esata, vis a vis USB 3, is dead. Again, sadly, given the overhead USB 
imposes.


Khalid:

Do you remember your test configuration?

I would not have thought any single non-SSD sata drive could saturate 
the link. I would have thought it even less likely over USB 3 - which is 
how I thought you were running things.

Thank you and Lori - it would not have occurred to me that a CPU/chipset 
would be designed/behave as nefariously as above for the dual bay docks.

You two seem to be pointing out that the SATA III 6Gbps spec. is a pipe 
dream - to get it every interconnection in the chain must be able to 
keep up, and if the 'bridges' themselves cannot ... I guess all I can 
say, again, is Caveat Emptor. I suppose.

Is this all really saying, for maximum speed, you're going to want to 
buy a dedicated sata controller card? But then you're going to be 
limited by bus speeds (PCIX?), anyways? Not to say that PCIX wouldn't 
keep up, but something in the chain won't? And, e.g. You can never feed 
it over that bus such that any sata link will get near max. spec?

Am I following any or all of this correctly?

On 14-08-05 06:32 PM, Khalid Baheyeldin wrote:
> On Tue, Aug 5, 2014 at 6:12 PM, John Johnson <jvj at golden.net> wrote:
>
>> Somewhere in the thread someone mentioned "This depends on your chipset.".
>>
>> All data transfers whether IDE, SATA & USB are channeled through the same
>> choke points in the chipset. (as mentioned Southbridge)
>>
>
> Yes.
>
>
> And when I was testing an SSD, and it turned out not to be faster (same ~
> 70MB/sec, from memory), Lori Paniak guessed that it was the Southbridge
> that was the bottleneck.
>
>
>
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