Date: Mon, 17 Nov 2014 14:50:44 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Brandon Vincent <Brandon.Vincent@asu.edu> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: OT-ish SATA port replicators vs. SAS "expanders" Message-ID: <20141117225044.GS24601@funkthat.com> In-Reply-To: <CAJm4238NDHV_uzertrrcce9kwFwyKoYY6pO5E58s-2DoZkwm-w@mail.gmail.com> References: <CACpH0Me7Y%2Bm6cENsg2otcP9agDp%2BwKPGnPxDafFfySPNkhsKBA@mail.gmail.com> <CAJm423_%2B5wL4G48ftVOmmkyyjSpekS3=sv801pyquRkqcz=fTQ@mail.gmail.com> <CACpH0MdfzpTXceHnRkAo60ztu4Bo%2BbKSpOYZJyV6goY0Q0TbUg@mail.gmail.com> <54693866.9040009@sentex.net> <CAJm4238NDHV_uzertrrcce9kwFwyKoYY6pO5E58s-2DoZkwm-w@mail.gmail.com>
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Brandon Vincent wrote this message on Sun, Nov 16, 2014 at 17:26 -0700: > On Sun, Nov 16, 2014 at 4:51 PM, Mike Tancsa <mike@sentex.net> wrote: > > I don think a port multiplier is the same as a SAS expander and a SAS/SATA > > controller does not necessarily support port multipliers. > > You're absolutely correct. The SATA specifications if I recall > correctly, outline that providing support for port multipliers is > optional. Not to mention, the vast majority of chipsets that do have > support for port multipliers only provide the slower command-based > switching method [1], The LSI SAS 2008 chipset is not what you > typically find on the cheap consumer "fake RAID" cards which most > people have [2]. > > Most people who purchase this card are purchasing it for SAS, true > RAID, performance, and reliability. Thus, LSI is only going to provide > support for the far superior SAS expander technology. If you go w/ SATA PMs, make sure you get a controller that supports FIS-base switching instead of command based switching... You'll get much better performance w/ NCQ support... As for if the LSI SAS 2008 will support FBS, probably not, as it'll require the driver and/or firmware to be aware of how to handle things... This page has a list which includes if the controller supports FIS/FBS: https://ata.wiki.kernel.org/index.php/SATA_hardware_features It doesn't list the Marvell 88SE9235 that I'm using (but not w/ PMs), but Marvell's site says it does, and it uses the ahci driver, which means it should if you have a new enough version of FreeBSD that supports PMs... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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