[Pc_Support] Re: eSATA RAID-1, putting the "IOP" outside the box -- IOPs, PCI[64|e|X] support and SATA cabling ...

[Bryan J. Smith]

Damien McKenna wrote:
> I was actually thinking of the Thecus N2050, not the Synology NAS:
> http://www.thecus.com/products_over.php?cid=1&pid=3

Yes, I know.  I've been changing the subject as appropriate in my past
correspondence too.

Damien McKenna wrote:
> This is an eSATA device that comes with a 33MHz/32bit PCI card.  Do
> you think its performance would improve if it was connected using a
> 66MHz/64bit card instead?

But what "commodity" SATA controllers do you know support PCI64 or PCI-X?
The overwhelming majority of SATA controllers are either PCI32 or PCIe x1.

Which brings us to the I/O processor ...

I don't know what I/O Processor they are using.  Their full-up NAS
product seems to use a 400MHz version of the 80219 X-Scale
(Superscalar ARM).

Now if you look at Intel's _current_ IOP line-up, pretty much all of
them support PCI64 or PCI-X.  Their "top-tier" IOP332/333 offer an
internal PCIe x8 to PCI-X bridge so you can use PCIe devices:
  http://www.intel.com/design/iio/index.htm

[ NOTE:  The clocks listed are _maximum_ for the product, _not_
typical/commodity ]

So, again, given the fact that pretty much every "commodity" SATA
controller is PCI32 or PCIe x1, they are stuck with PCI32.  Unless
they want to fork out the dough for a IOP332/333.  Yes, it might cost
sub-$30 in quantity, but that's a far cry in margins from the sub-$10
cost of other IOPs.

Damien McKenna wrote:
> Further, is there any reason why this would not work when connected
> to a plain SATA connector rather than an e-SATA connector (using a
> converter cable)?

Nope, as long as you consider the fact that SATA can't go farther than
1m -- at least at 1.5Gbps.  SATA 3.0Gbps was supposed to be
twisted-pair and not "flat", so it might even be shorter in lenght --
like half.  And that's before considering interference/signal loss in
connectors.

eSATA is supposed to be better shielded for 2x length.  Don't know
since SATA is still used internally.

SAS uses differential serial logic to go 8m.  You can also trunk 2, 4
or 8 pair for 6, 12 and 24Gbps aggregate.  SAS can fall back to SATA
as well.

You can think of SAS like LVD SCSI and SATA like SE SCSI -- almost literally.