questions about a PERC in a 2950

Chris Stromsoe cbs at
Tue Oct 16 19:22:30 CDT 2007

On Tue, 16 Oct 2007, J. Epperson wrote:
> On Tue, October 16, 2007 12:39, Chris Stromsoe wrote:
>> I'm not a fan of hardware raid.  Getting the data off the drives if 
>> something goes very bad can be challenging.  With 8 cores in the box in 
>> question, I'm not lacking for CPU.  The management tools leave quite a 
>> bit to be desired, not the least of which is that there isn't a simple 
>> proc or sysfs interface for managing the driver (using sh and echo to 
>> manage drive replacement, rebuilds, hot spares, etc, with cat for 
>> reading back controller and drive status would be perfect).  I'm also 
>> running Debian and there isn't a Debian native build of the management 
>> tools or available source to build them myself.
> I get most of that, but is getting data off a hosed software raid array 
> any simpler than with hardware raid?  You seem quite knowledgeable, want 
> to understand your perspective.

Having done both, getting data off a hosed software raid5 was easier. 
Not significantly easier, but easier.

I'm not really all that concerned with having to retrieve the data after 
the controller croaks, as far as software vs. hardware.  It's more that 
having a raid controller adds an additional layer of complexity to the 
setup, and makes it that much harder to know why something went wrong when 
it eventually does go wrong.

The hardware controller is fixed.  It does raid in a particular way, and 
that's it.  You'll get firmware updates that might fix bugs.  I say might 
because, well, maybe the updates don't actually fix bugs; look back 
through old list archives for the PERC4 series cards [rebadged LSI 
MegaRaid something or other] and how many iterations of firmware updates + 
kernel versions + spilling of chicken blood and voodoo magic it took to 
get a system that was stable under very high load.

The MD subsystem has, in the last handful of years, gained a ton of 
features, and all of them made available with a kernel build and a new 
mdadm release.

In any event, software raid is "free", easy, and stable for my use cases, 
while hardware raid is expensive, requires a specific environment in order 
to be supported, and has proven problematic in the past.


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