SAS Drive Numbering inside the MPT driver

[Josef Grosch]

On Wed, Apr 09, 2008 at 10:23:07AM +1000, Damian McGuckin wrote:
> On Mon, 7 Apr 2008, Josef Grosch wrote:
> 
> > I really can't answer your question. We tried the LSI controller and had 
> > a couple of problems. I think this was one of them. We have settled on 
> > the Adaptec 3805 which is an 8 port controller. We are very happy with 
> > this controller. It's fast, stable and well supported in FreeBSD.
> 
> With this, if you want to use it JBOD, don't you have to create fake RAID 
> volumes on each drive. Initially this is
> 
> 	Drive0	Volume0
> 	Drive1	Volume1
> 
> etc.  Does FreeBSD use the Volume numbers at all when assigning drive IDs
> 
> 	/dev/da0
> 	/dev/da1
> 	....
> 	/dev/daN
> 
> or does it work purely from the slot position?
> 
> Many Thanks - Damian

We have not used JBOD as such. We mostly use RAID 0, 1, 5, 10. I fooled
around with JBOD with each disk being stand alone. The controller presented
each disk as a separate device ie. da0, da1 ... daN. So, no, you do not
have to RAID a disk if you want stand alone. I did this when testing ZFS on
7.0. 

The controller labels the disk with something the controller sees but the
OS does not. I know this because I moved, these are hot swap units, a disk
from one slot to another and the controller told me that the label did not
match the slot number. I assume the controller relabeled the disk or more
correctly updated it's internal map because it never complained again.

That being said, the controller presents the OS with a device and hides the
details from the OS. I have had a number of situations where I have 6
drives in a RAID 10 and had to move disks around from their original
slot. The controller bitched once but the OS, FreeBSD 6.2, 6.3, 7.0 saw the
RAID as one disk with one device. It never knew that the disks had been
moved around. 

We at Juniper have a long history of using Adaptec controllers. I have
about 200 servers using the 3805 and, except for outdated firmeware, have
never had a problem with them. I think if you start using the 3805 it will
be one less thing to think about and you can go back to putting out all the
other fires you are fighting ;-)


Josef

-- 
FreeBSD 6.3         |
Josef Grosch        | You can't expect to wield supreme executive power
jgrosch at juniper.net | just 'cause some watery tart threw a sword at you!