I hope that you're not feeling too bad today!
I've successfully installed RAID on a very similar setup to the one you are
using so I expect that we can work this out.
I had a motherboard with a Highpoint based chipset on it. These are similar
to the Promise chipset you describe. In both cases the chipset doesn't
"really" do RAID. Instead it is really much like a normal dual IDE
interface and the RAID mirroring or striping is being done by a driver in
software. The physical difference is down to some resistor somewhere (I
have heard). Plus there is a BIOS interface that you can activate by
pressing Ctrl-H when you boot, allowing you to go into a BIOS type blue and
white (or was it yellow?) screen that enables you to define RAID1 mirrors,
RAID0 stripe sets, create and break mirrors, etc.
The driver is then supposed to take over where the BIOS left off when the
operating system gets started. As I understand it this means that these
"semi-software" RAID systems work in a fundamentally different way from what
I had traditionally regarded as RAID.
For a RAID 1 mirror (for instance) on a "real" or "hardware" RAID solution,
the operating system (be it Windows 3.1, DOS, FreeBSD, Slackware Linux,
Fedora Core, SuSE Linux, Windows ME or Windows 2003 Server) sees what looks
to it like one normal hard disk on one of it's SCSI interfaces (not aware if
this "hardware" RAID ever exists on IDE but if so then the "disk" would
appear as a master or slave on one of the IDE interfaces). When the OS
writes a block to the hard drive the data is in fact sent to a
microcontroller on the RAID card. This microcontroller then decides what to
do with the block, based on how the actual physical disks attached to the
card are configured, in the case of RAID1 it will write the block to both
disks, or if reading, will decide one disk to read from (based on the head
that is currently nearest).
On a "semi-software" card (or motherboard) like the Promise and Highpoint
based ones all this work is done by the operating system driver. The
operating system can actually see both disks in a RAID1 mirror as normal,
seperate disks. (You can often see this in the custom partitioning section
of YaST as two separate disks, perhaps /dev/hde and /dev/hdg.)
There are a few consequenses to this (as I learned to my cost earlier this
year). Firstly the Promise/Highpoint are a lot cheaper to buy, which is why
we got them, when we didn't know the difference. Secondly they usually
don't support RAID4 or 5, although I guess that may change as I can't see
any reason why they can't in principle. Thirdly your OS driver *must* be
100% supported, stable and reliable.
To my cost I installed a Linux driver that should have worked on one of our
business systems. Thank God we had a good backup solution in place, it
worked beautifully for a day or so then merrily trashed the drive in
question which had to be rebuilt from scratch. Who knows, maybe I didn't
have exactly the perfect version of the driver or maybe I needed to perform
some undocumented step to ensure that this didn't happen. Anyway you get my
point, I'm a Linux sysadmin, not a developer, I don't get paid to install
stuff that will trash our precious business data.
Because this setup operates in software...
1) you must have working drivers for all OS partitions
2) these partitions will be mirrored independantly, the driver on Windows
2000 will work seperately from the one on Linux
3) the performance will be no better than any other software RAID, quite
possibly the performance will be worse
With Win 2003 (at least) this works pretty much transparently as you have
seen.
With Linux what I'd recommend is that you forget about the Promise driver
and use the Software RAID capabilities built into SuSE Linux. The
configuration guide should give you enough help on how to do this, if not
then by all means come back to this list for help.
I switched to standard Linux Software RAID and I've literally never looked
back, I do not miss the BIOS utility and the nagging concern that the 3rd
party driver might mess up and trash my disks any day. Remember that the
Software RAID in Linux has effectively been far more thoroughly tested than
the Linux driver that Promise supply.
Good luck,
Carl Peto
----- Original Message -----
From: "Eveline Bernard"