Re: ld vs sd on cac/ciss/aac and friends

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Fri, May 28, 2010 at 10:25:46PM -0400, Chris Ross wrote:
>
>   I am building a machine with a ciss(4) in it, to replace an older  
> Compaq that has a cac(4) in it.  I noticed, and was surprised, that the 
> ciss(4) presents the volumes as sd(4) devices rather than ld(4) devices.  
> My cac's and aac's present ld(4) devices, which makes sense, as that's 
> largely what ld(4) means.

Some RAID controllers actually present a SCSI "bus" to the host, with SCSI
connection, disconnection, queueing, etc. semantics.  On controllers that
do this, it's considerably more work to *not* present the logical volumes
as SCSI "disks" than to do so.

On the other hand, drivers that fake up SCSI when the underlying device's
firmware isn't doing SCSI at all... that's gross.  I don't think we have
any of those in the tree at the moment, however, do we?

Thor