Re: HostRaid support on FreeBSD

Søren Schmidt wrote:

> 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.

But I assume that on-disk format of this info and its location is 
controller-dependent, so that appropriate code to read/decode this info 
should probably be in the controller's driver.

-Maxim