Date: Tue, 16 Feb 2016 08:55:35 -0700 From: Alan Somers <asomers@freebsd.org> To: David Ford <david.ford@ouce.ox.ac.uk> Cc: "freebsd-scsi@freebsd.org" <freebsd-scsi@freebsd.org> Subject: Re: camcontrol sata affiliations Message-ID: <CAOtMX2hf_Od_Xdq6d8Hi70=gXdKMZPRusHbU22hxo=wwHNeWtg@mail.gmail.com> In-Reply-To: <D64F8B312592434E801895942B9101163F9C7DFF@MBX01.ad.oak.ox.ac.uk> References: <D64F8B312592434E801895942B9101163F9C7A61@MBX01.ad.oak.ox.ac.uk> <CAOtMX2jvVLUFHcpOs1r=Wcr_G3rKFStDQ92RatSsq-VAM9FDmQ@mail.gmail.com> <D64F8B312592434E801895942B9101163F9C7DFF@MBX01.ad.oak.ox.ac.uk>
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On Tue, Feb 16, 2016 at 8:32 AM, David Ford <david.ford@ouce.ox.ac.uk> wrote: >> -----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 > Only if you have a JBOD that uses a single expander chip for both hosts. Then I think those commands would do what you want.
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