Re: [gentoo-user] Knoppix Install Method

[Jim Burwell]

Drew Tomlinson wrote:

> On 12/10/2005 1:17 PM Stroller wrote:
>
>>
>> On Dec 10, 2005, at 5:08 pm, drew@××××××××××××××.net wrote:
>>
>>>
>>> I have a system on an Abit motherboard with the Nvidia GeForce 4
>>> chipset.
>>> There are two SATA disks in a hardward stripe configuration using the
>>> controller built in to the motherboard.
>>> ...
>>> I booted the latest Knoppix dated 9/23/05 and see two
>>> icons on the desktop for my drives.  One for sda the other for sdb.
>>> I can
>>> not mount either.  I assume this is because Knoppix is seeing each
>>> drive
>>> individually instead of the one logical striped drive it is.
>>
>>
>>
>> I'm no expert on this, but I believe that many ATA "hardware" RAID
>> arrangements in fact just use their Windoze drivers to do software
>> RAID. I'd do some research via Googling the chipset &/or board's
>> model number if I were you.
>
>
>
> I haven't found anything yet but then I haven't looked real hard.
> However I suspect this does not rely on any Windows drivers as the
> controller is managed long before Windows boots.  Just after POST and
> before the OS starts, a brief message showing the controller is
> displayed.  By pressing F10, I can manage my stripe.  Much like I see
> most SCSI cards.


Stroller is right on this one.  Most built-in motherboard 'RAID chips' 
and inexpensive RAID cards are simply software RAID with a BIOS front 
end that can be used to create/manage RAID volumes composed of attached 
disks.  The firmware for these RAID chips/cards simply scans each disk 
for its proprietery RAID metadata, and presents any found volumes as a 
drive to the BIOS.  They also often detect problems with the arrays 
(missing components, etc) and present the user with boot time options to 
deal with these situations (boot in degraded mode, replace missing 
component and sync, etc).  But the actual block-by-block RAID operations 
(writing mirror blocks, computing/reading/writing parity data, degraded 
operation, etc) are done in a device driver under the OS, once booted.  
The CPU is doing all the RAID heavy lifting with these arrangements.  I 
see these sorts of RAID solutions as merely glorified IDE or SATA 
controllers with some advanced firmware in front of them.

True hardware RAID do these block-by-block operations on a dedicated 
controller, often with some sort of NVRAM write-behind/read-ahead cache 
between the OS and the volume, which can survive sudden power 
loss/crashes, etc.  The RAID volumes presented to the boot time 
environment and OS look like regular drives.  The RAID controller 
hardware does the RAID heavy-lifting (parity computation, re-syncs, 
etc), offloading them from the CPU.  Obviously these hardware RAID 
solutions are more sophisticated than the cheap software RAID 
arrangements, which is why presently, you won't find one for less than 
about $400 (USD), where you can find the software RAID cards for < $100 
(USD).

Both types seem to present a similar user interface to the user, which 
is cause for confusion.  Also, the vendors of the cheap RAID solutions 
don't go out of their way to inform the customers of the differences 
between their stuff and the hardware RAID solutions, of course, which is 
more cause for confusion.  :-)


>>> Is there some magic I can perform at the boot prompt to get Knoppix
>>> to see the
>>> two individual drives as one logical striped drive?  I can't recover
>>> the data
>>> from booting Windows because it's all screwed up and reboots itself
>>> shortly
>>> after logon.
>>
>>
>>
>> If my guess is correct then the best thing might be to install
>> Windows on a spare drive & boot from that to see the RAID as one. You
>> might try booting with a Windows CD & see if the RAID is recognised
>> as a single partition... if you get the option to do a repair install
>> you _should_ be able to get an at-least-mostly-working Windows
>> install & all your data intact. Recover the data to a portable drive
>> & format.
>
>
>
> Thanks.  I tried an overlay install again and things seem to be going
> well.  Copying data now.
>
> Thanks for your ideas!
>
> Drew
>

As mentioned by another poster in this thread, there is also the 
somewhat too generically named 'dmraid'.  (When I first stumbled across 
this, I thought it was some LVM2 native replacement for the good 'ole 
Linux RAID [md] devices.  I personally think it should be given a more 
specific name like 'metaraid' or 'omniraid' or soemthing like that, but 
I digress). 

You may have been able to use this to mount your striped volume.

 From my admittedly brief reading, dmraid appears to be a metadata 
agnostic device mapper based software RAID driver.  That is, it can 
understand and operate RAID volumes created using many vendors' software 
RAID chips and cards and their proprietary metadata formats by itself, 
without the need to install drivers from individual vendors.  Pretty cool!

However, the userspace tools for dmraid are presently keyword masked in 
gentoo, and the somewhat sparse documentation for dmaid seems to 
indicate that it's not quite ready for prime time yet.  Looks 
interesting though.


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