[NTLUG:Discuss] RE: true hardware/intelligent ATA RAID -- clarification.

[Bryan J. Smith]

On Thu, 2004-07-22 at 07:42, Bryan J. Smith wrote:
> Again, it's _nothing_ more than a ATA chip, that's it.  When your system
> boots, the 16-bit BIOS "hides" the real disk configuration.  The second
> the 32/64-bit kernel boots, it sees the disks "raw" and there must be a
> software driver to understand the organization.
> If not, the system panics.

Actually, it's worse than that.  On some OSes, you can lose the existing
RAID volume.  How?  Because the OS will see the "regular" ATA disks and
could possibly write to them (typically DOS/NT-based, not Linux).

Yes, you will get a kernel panic if you do not load the driver for any
other cards as well, even intelligent RAID cards.  But at least the
volumes are "protected" and "not seen."  With FRAID cards, the "raw" ATA
disks become viewable to the OS.

My points are 5-fold:

1)  If you have  a FRAID card but no 32/64-bit OS driver, you will see
the disks "raw" and possibly destroy the RAID volume (if the OS or you
modify them).  I've seen this time and time again, especially when
someone is trying to install Linux or even a newer NT-based Windows
where they didn't load the driver disk.

2)  The FRAID software drivers have 100% of the intelligence in them and
you will _never_ find GPL drivers from the vendor.  The GPL ataraid
"core" and related "reverse engineered" vendor drivers are _not_
recommended, especially for newer cards that have not been tested as the
_do_ change.

3)  A true hardware, intelligence RAID card has a simple block driver,
because 100% of the RAID intelligence is on the board.  It _always_
appears as either a volume (with a driver) or not at all.  The 3Ware
3w-xxxx GPL driver has been in the stock kernel since 2.2.15 (yes,
_2.2_).  It's nice to boost _any_ distro's disk and get support
out-of-the-box.

Now I always make sure my 3Ware firmware, driver and 3DM versions match.
You always want to do that with any intelligent storage card.  But I've
booted older kernels and older drivers without issue.  I just wouldn't
pull up 3DM to do any real-time maintanence unless the drivers/3DM are
at least as current as the firmware on the card.  Again, you'll have
that issue with any, intelligent card (or FRAID for that matter).

Since most vendor kernels ship the latest 3Ware driver, I _rarely_
have an issue when upgrading.  And if I find it's not quite the latest,
I still boot the kernel, then compile the 3Ware driver and either reload
it (if it wasn't my boot device) or reboot.  I do _not_ have to build an
entire kernel -- the 3Ware Makefile is intelligent enough to build
itself without a full kernel rebuild (although you need to have the
kernel source installed so it can look at things).

The 3Ware volumes are also inter-compatible because 3Ware _always_
maintains 100% backward compatibility with its volumes.  E.g., I've even
taken a Escalade 5000 volume and moved it to a 7000 series card.  That
is why I have been most impressed with 3Ware -- _unlike_ a lot of
vendor's cards.  I've been able to move volumes around temporarily, or
entirely to a new system (without a rebuild!).


-- 
     Linux Enthusiasts call me anti-Linux.
   Windows Enthusisats call me anti-Microsoft.
 They both must be correct because I have over a
decade of experience with both in mission critical
environments, resulting in a bigotry dedicated to
 mitigating risk and focusing on technologies ...
           not products or vendors
--------------------------------------------------
Bryan J. Smith, E.I.            b.j.smith at ieee.org