HostRaid support on FreeBSD

[Søren Schmidt]

Maxim Sobolev wrote:

> Well, my knowelege about internals of software RAID controllers is quite 
> limited, but as long as I know they are no more than BIOS with UI for 
> setting up RAIDs and interface to main BIOS that hides internal RAID 
> structure allowing to boot off the RAID. Also they provide some 
> persistent storage for RAID configuration, I assume either in some 
> controller's NVRAM or on the HDDs. Therefore, the same set of GEOM RAID 
> modules can work with different software RAID controllers (SCSI, ATA, 
> SATA etc) if there will be a standard way to extract this info from the 
> controller's driver, and present it in some common format. That's what I 
> am talking about.

Well, I dont know about SCSI, but ATA/SATA always stores the metadata on 
disk, the controller has nothing todo with the RAID functionality, its 
merely a way to talk to the disks.

Reading the metadata off the disks and using that info to access a RAID 
array is easy and can be had even without docs in a few hours. Writing 
back the metadata in case of failures etc to retain sanity of the array 
is "somewhat" more difficult. Actually I'm working with this currently 
for new formats for ata-raid and its not trivial to get right.

-- 
-Søren