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Date:      Wed, 17 Feb 2016 14:18:16 -0600
From:      Doug McIntyre <merlyn@geeks.org>
To:        David Ford <david.ford@ouce.ox.ac.uk>
Cc:        "'freebsd-questions@freebsd.org'" <freebsd-questions@freebsd.org>
Subject:   Re: multi-homed drive SATA drive affiliations
Message-ID:  <20160217201816.GA50395@geeks.org>
In-Reply-To: <D64F8B312592434E801895942B9101163F9C5898@MBX01.ad.oak.ox.ac.uk>
References:  <D64F8B312592434E801895942B9101163F9C5898@MBX01.ad.oak.ox.ac.uk>

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On Thu, Feb 11, 2016 at 03:23:31PM +0000, David Ford wrote:
> I suspect I'm missing something obvious here, but I can't quite think what. I have a set of SAS disk shelves which are each dual homed to a pair of FreeBSD 10.1 systems... 
> The problem is that for SATA drives (the idea is the use SSDs for L2ARC/ZIL) SATA affiliations don't appear to be having the desired effect, the disks get assigned to one host when they are attached..
..

Are you using SAS Interposer boards on each of the SATA drives, or are
they plugged directly into the SAS backplane?

The only way SAS dual channel works is the SAS disks have additional
pins on the connector, so they can talk out either port, while SATA disks only
have one set of pins/port out to talk.

Typically, a disk vendor if using SATA drives or other single-port
limited hardware would install a SAS Interposer board on the backside
of the SATA disk, so that it can talk dual port out to the SAS
backplane.

Ie. on Dell systems, they have disk trays with screw mounts that are
labelled SAS (which butt the drive right up to the connector), or are
labelled SATA, where it leaves room to mount a SAS interposer board, such as

http://www.ebay.com/itm/USED-DELL-SATA-to-SAS-CN-0PN939-13740P15945-06-A-Server-Interposer-Board-/311518244215?hash=item4887ef2d77:g:6NkAAOSwAYtWKEwX

on the backside of the tray. I've also seen trays like this on all the
major storage vendors, but not so much any longer, since SAS SSD's are
somewhat afordable now-a-days.






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