camcontrol sata affiliations

[Alan Somers]

On Tue, Feb 16, 2016 at 8:32 AM, David Ford <david.ford at ouce.ox.ac.uk> wrote:
>> -----Original Message-----
>> From: asomers at gmail.com [mailto:asomers at gmail.com] On Behalf Of Alan Somers
>> Sent: 16 February 2016 15:23
>> To: David Ford <david.ford at ouce.ox.ac.uk>
>> Cc: freebsd-scsi at 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.