Date: Tue, 16 Feb 2016 15:32:30 +0000 From: David Ford <david.ford@ouce.ox.ac.uk> To: 'Alan Somers' <asomers@freebsd.org> Cc: "freebsd-scsi@freebsd.org" <freebsd-scsi@freebsd.org> Subject: RE: camcontrol sata affiliations Message-ID: <D64F8B312592434E801895942B9101163F9C7DFF@MBX01.ad.oak.ox.ac.uk> In-Reply-To: <CAOtMX2jvVLUFHcpOs1r=Wcr_G3rKFStDQ92RatSsq-VAM9FDmQ@mail.gmail.com> References: <D64F8B312592434E801895942B9101163F9C7A61@MBX01.ad.oak.ox.ac.uk> <CAOtMX2jvVLUFHcpOs1r=Wcr_G3rKFStDQ92RatSsq-VAM9FDmQ@mail.gmail.com>
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> -----Original Message----- > From: asomers@gmail.com [mailto:asomers@gmail.com] On Behalf Of Alan Somers > Sent: 16 February 2016 15:23 > To: David Ford <david.ford@ouce.ox.ac.uk> > Cc: freebsd-scsi@freebsd.org > Subject: Re: camcontrol sata affiliations > > You aren't missing anything. This is just a difference between SATA > and SAS. SAS drives have two ports, and SATA drives have only one. > Most (all?) multipath JBODs like yours have two separate expander > chips. They connect every slot's first port to the first expander and > every slot's second port to the second expander. That results in a > chassis with no SPOF. With such hardware, there's no way to connect a > SATA drive to both servers. And with more complicated hardware that > uses a single expander chip combined with SAS zoning to connect a SATA > drive to two servers, you're stuck with a SPOF. Thanks that at least clarifies what's going on. I had understood most of that, however I thought that the idea of the ability to clear the affiliation was to permit the second expander to take over. I suspect I was mistaken. Thanks David
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