hardware raid solutions?

[David Abrahams]

Eric,

you obviously have more experience with raid than I do, so I hope you
don't mind if I ask a few direct questions...

"Eric S. Johansson" <esj at harvee.org> writes:

> Software raid (mdX) does work well most of the time.  Unfortunately, I
> have had failures due to crashes, power outages etc. where the raid
> array doesn't reconstruct.  In raid 1, I was left with two discs that
> were different but neither was obviously bad and I couldn't tell which
> was the right one hence my move to raid five.

Makes sense.  But how does this relate to the software-vs-hardware
raid debate?  You can do raid 5 in software just as in hardware, no?

> Software raid also has problems when you're doing anything disk
> intensive like backup every hour or two.  Yes, hardware has similar
> problems but is not my CPU that's being eaten alive.  :-)

I am setting this raid up on a machine that will be used for large
build/test runs.  That can get disk- and compute-intensive, so I
suppose that issue could be relevant to me.

> So, convince me that I can use a software raid solution for my system
> for all partitions and still be able to boot if the raid array has
> failed (total failure, one disk, or 2 disk).

Sorry, but I must be missing something important.  How can you expect
to boot if your disk storage has *total* failure?

> if I were to use software raid, I would break up the large disks (200
> GB) into 50 GB physical partitions, Raid physical partitions (from
> different disks duh), 

Does "raid physical partitions" mean you'd set up raid 1 mirroring
across pairs of real physical partitions?

> LVM the raid physical partitions together 

Meaning you'd create an LVM volume group containing all the "physical
partitions" presented by software raid?

> and then create logical volumes for all of my system partitions.
>
> the reason for the strategy is that if rate needs to reconstruct, it
> will take less time to rebuild an individual partition than the entire
> disks.  

Ah, I think that's not a strategy I could expect to use with dmraid,
because IIUC it will only allow me to create raid 1 mirroring across
whole disks.

> If all need to be rebuilt, well it's part of a very painful
> experience.  ;-)
>
> also convince me that there's a good notification process that
> something has failed.

That's an issue with hardware, too, innit?  You probably need some
kind of software monitor to go along with it.

> I'm willing to be convinced.  Make your best argument for the software
> raid.  And failing that, hardware cards suggestions would also be
> welcome.  :-)

Me too.  I'm still trying to gather as much information as possible
before I waste another week on dmraid.  Thanks in advance for your
answers.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com