zpool degraded - 'UNAVAIL cannot open' functioning drive

[Antony Mawer]

On 10/08/2008 5:11 PM, Jeremy Chadwick wrote:
> On Fri, Aug 08, 2008 at 08:23:41AM +0400, Andrey V. Elsukov wrote:
>> Jeremy Chadwick wrote:
>>> It would be benefitial if there was some form of sysctl to increase the
>>> verbosity from the ATA subsystem when an error happens.  The existing
>>> data we get back is terse, and barely useful.  I know for a fact there's
>>> more debug information that could be output in such scenarios.  And
>>> please do not reply with "good idea, send patches" unless you're wanting
>>> to be chewed out.  :-)
>> Ok, I'll try to add some verbose 'printfs' in my branch in perforce :)
> 
> This also starts to enter the realm of why FreeBSD does not implement
> support for NCQ -- is this because the ATA driver was built solely
> around ATA, rather than AHCI?  Linux appears to have two different
> drivers depending upon if you're using AHCI or not.  FreeBSD's ata(4)
> code seems to have everything intermixed/jumbled around, so it looks a
> lot like spaghetti...  Is this the problem?

My understanding of it is that the "legacy" style SATA support is 
modeled off ATA, while AHCI implements more SCSI-like features (like 
NCQ). With AHCI mode on Linux, I believe it uses the SCSI subsystem 
where the infrastructure for things like tagged queuing are available.

I thought I heard Scott Long was looking at implementing a SATA 
subsystem based on CAM at one point, but I gather it succumbed to ENOTIME...

--Antony