On Sat, 2005-06-18 at 16:58 +0200, Dag Wieers wrote:
> Hi,
> On my x86_64 system I have a SiL311x controller that can do RAID. If I
> configure my 2 identical disks in a RAID1 setup, I would expect to see
> only 1 block device on Linux. Still I see 2 block devices.
> Is this intentional, and if so, isn't that dangerous ? (i.e. writing to
> both disks at the same time)
> Anyone with an insight, please explain :)
They are _not_ RAID, they are what I call "Fake/Free RAID" (FRAID).
The BIOS just allows you to designate the disks as RAID-1 (simple
mirroring) or organize the blocks into RAID-0 (stripped). Once the OS
loads, it not only needs to know that so it doesn't see the disks as
"just a bunch of disks," but so it knows how to write the data as such.
That is done 100% in the OS driver.
Since that logic is typically licensed from the same 2-3 3rd parties,
and those 3rd parties make royalties on those sales, it is _never_ going
to be GPL.
Now there is a "clean-room" GPL RAID logic in "ataraid.c" in the kernel.
And then there are "card interface" sister drivers in "hptraid.c" (HPT),
"pdcraid.c" (Promise) and "silraid.c" (Silicon Image), but they _rarely_
work well. Little changes and differences in the cards, drivers, etc...
always seem to cause all sorts of issues when I've tried them.
_Real_ hardware RAID cards _never_ talk directly to the ATA channels.
They _always_ have _all_ communication between the system and the ATA
channels go through an "on-board intelligence" like an i960
microcontroller in the Promise SuperTrak, Adaptec 2400/2800A, LSI Logic
MegaRAID 320-4 and 320-6, an XScale superscalar microcontroller in the
LSI Logic MegaRAID 320-8X, or an ASIC in the 3Ware Escalade and NetCell
SR-series.
For more on ATA RAID, see the article "Dissecting ATA RAID Options" in
2004 April "Sys Admin" magazine. The article is not available on-line,
but if you subscribe to Sys Admin, you get a CD with _all_ back issues
of Sys Admin and Perl Journal:
http://www.samag.com/articles/2004/0404/
--
Bryan J. Smith b.j.smith@xxxxxxxx
---------------------------------------------------------------------
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will also penalize you similarly (to those below you, and then below
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mentary concepts of limits, is mutually exclusive with US journalism.
So forget even attempting to explain how tax cuts work. ;->
