Switchover to CAM ATA?

[Bernd Walter]

On Fri, Apr 23, 2010 at 09:50:33AM -0400, John Baldwin wrote:
> On Thursday 22 April 2010 11:31:37 am Alexander Motin wrote:
> > If ataraid(4) should be reimplemented in GEOM, then how exactly? One
> > more separate RAID infrastructure in GEOM (third?) looks excessive.
> > Reuse gmirror, gstripe,... code would be nice, but will make them more
> > complicated and could be not easy for RAID0+1 (due to common metadata)
> > and RAID5 (due to lack of module in a base system).
> 
> Scott's view (which sounds good to me) is that GEOM should include a library 
> of routines for working with common transforms such as RAID1, striping, etc.  
> Each ATA RAID vendor format would then consist of a small GEOM module that 
> used the library routines to manage all the I/O and the bulk of the module 
> would be managing a specific metadata format.

I remember that SCSI standard has support for xor read-modify-write
operations in addition to normal read/write to reduce R5 latency and
bandwith.
I'm not sure if any devices actually support it, but I think this
may be worthwhile for networked devices.

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.