[PC-BSD Testing] Support for J-Micron?

Josh Paetzel josh at tcbug.org
Wed Dec 2 04:21:51 PST 2009

On Dec 2, 2009, at 1:09 AM, Jeff <dejamuse at yahoo.com> wrote:

> I tried that at first but ad0 and ad1 are the two main drives and  
> I'd assume they'd be the same since it's a RAID-1, mirrored.
> Mounting either of those drives shows the contents of the system.

Couple of things:

The last eSATA controller I had didn't support hot plugging in  
FreeBSD. A drive attached when the system booted would be seen, but  
the system would not recognize drives attached after the system was  

PATA supports two devices per controller, generally refered to as a  
master and a slave. The controller cannot access both devices  
simultaniously. In a perfect world the devices in your mirror would be  
on seperate controllers. I don't know how smart the ar driver is about  
reads, but theoretically having the drives on seperate controllers  
would allow for two concurrent reads simultaniously.  It could also  
allow for better resiliancy in the case of an unclean shutdown. In  
your current setup, writes are always serialized. If the system were  
to crash during a write the mirror would almost certainly need to be  
resynced.  Anyways, you might contemplate moving the drive that is the  
primary slave (ad1) to being on the other IDE controller. It may or  
may not have some tangible benefits, in theory it should.


Josh Paetzel
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