HostRaid support on FreeBSD
sobomax at portaone.com
Wed Jun 23 15:18:19 GMT 2004
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.
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