[geeks] Cheap Dell Servers

[nate at portents.com]

>> No, as I said, there's a theoretical upward limit of 15, but in
>> practice
>> they implement the port multipliers supporting 5 drives.
>
> But isn't that just sharing a single link for the channels, but still
> connecting them 1:1 with their controller ports?

I would argue that in the situation where FIS based switching is used by
the port multiplier, the relationship is no longer 1:1.  Specifically:

"FISbased switching offers high performance storage connections to
multiple drives simultaneously. The host issues and completes commands to
drives at any time. The port multiplier will direct data to any drive
ready for I/O. An arbitration algorithm ensures a balanced data flow.
Unlike Command-based switching, FIS-based switching allows aggregation of
reads to fully use the higher bandwidth of the 3Gb/s host link and takes
full advantage of the performance benefits of Native Command Queuing (NCQ)
on the port multiplier, resulting in aggregated throughput of up to
300MB/second."

- Nate