SATA Port Multipliers in FreeBSD (6.3)

[Christopher Key]

Daan Vreeken wrote:
> Hi Christopher,
>
> On Thursday 05 March 2009 15:25:35 Christopher Key wrote:
>   
>> Hello,
>>
>> I'm looking to substantially expand the storage on my FreeBSD 6.3 home
>> media server.  With regards hardware, the simplest way to attach large
>> numbers of drives seem to be to use SATA port multipliers, but I've been
>> unable to find any consensus on their level of support in FreeBSD.  I'm
>> currently looking at a RocketRAID 2314 and SiI3726 based port
>> multipliers.  Has any had any experience with this combination?
>>     
>
> The Sil3726 works very well if you run a recent enough version of FreeBSD. We 
> use the device in a custom storage appliance. I don't know the RocketRAID 
> 2314 though. You need a SATA 2.0 controller for Port Multipliers to work.
>
>   
I'm pretty sure the RocketRAID 2314 is a SATA 2.0 controller.  I've 
references in places to it supporting port multipliers, but have been 
unable to to find any further details on quite what this means.  To be 
honest, I don't fully understand how the ATA system fits together.  
HighPoint offer a FreeBSD driver, but I don't know whether this replaces 
functionality within FreeBSD, or is an additional requirement.  Nor do I 
know whether port multiplier support is the responsibility of the ATA 
driver, the ATA controller, both or either, nor whether the ATA 
controller being a RAID card in JBOD mode affects anything.  I was 
thinking that for the RR2314 to work with port multipliers whilst it was 
doing hardware RAID, it must fully understand how to address drives 
behind a port multiplier and might do the same in JBOD mode, simply 
presenting the ATA driver with a list of drives.  Whether this is valid 
reasoning, I've no idea.
> FreeBSD has (experimental) support for Port Multipliers since the following 
> commit :
>
> On Thursday 10 April 2008 15:05:05 Søren Schmidt wrote:
>   
>> sos         2008-04-10 13:05:05 UTC
>>
>>   FreeBSD src repository
>>     
> ...
>   
>>   Log:
>>   Add experimental support for SATA Port Multipliers
>>
>>   Support is working on the Silicon Image SiI3124/3132.
>>   Support is working on some AHCI chips but far from all.
>>
>>   Remember this is WIP, so test reports and (constructive) suggestions are
>> welcome!
>>     
Thanks, I've found the relevent revision in SVN,
http://svn.freebsd.org/viewvc/base?view=revision&revision=178067

I'll read through the diffs to see if I can get a better idea of how 
everything works.

Kind Regards,

Christopher Key