Date: Sat, 15 Nov 2014 18:08:38 -0800 From: Darren Pilgrim <list_freebsd@bluerosetech.com> To: Zaphod Beeblebrox <zbeeble@gmail.com>, FreeBSD Hackers <freebsd-hackers@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: OT-ish SATA port replicators vs. SAS "expanders" Message-ID: <54680726.1010708@bluerosetech.com> In-Reply-To: <CACpH0Me7Y%2Bm6cENsg2otcP9agDp%2BwKPGnPxDafFfySPNkhsKBA@mail.gmail.com> References: <CACpH0Me7Y%2Bm6cENsg2otcP9agDp%2BwKPGnPxDafFfySPNkhsKBA@mail.gmail.com>
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On 11/15/2014 2:42 PM, Zaphod Beeblebrox wrote: > First... seriously... whoever was working on this naming convention thought > "expanders" was a good name? [...] > What is the real difference? Is it possible to hack the driver to support > (obviously not booting from) SATA port replicators on the LSI? Yes, the nomenclature isn't great. In short: An SAS expander is basically a multi-lane version of fibre channel without all that WWN nonsense. You usually get two or four SAS lanes per port. These are external with fancy cables. SAS expanders are often simply labelled as "external SAS port". A SATA port replicator (or port multiplier) is more like a USB hub: you plug the replicator into a host SATA port and it provides more than one SATA port for devices. I've yet to see one without interoperability problems. They also add a big risk: if one of the devices on a replicator has a problem, the host can't reset individual replicated ports--just the host port.
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