[ale] Onboard RAID

[Pat Regan]

On Wed, 16 Nov 2011 18:28:08 -0500
Brian Mathis <brian.mathis+ale at betteradmin.com> wrote:

> Yes, I do have such knowledge.  It's called using a supported,
> enterprise-level RAID card with a warranty.  Any server admin worth
> their salt is using equipment from a large manufacturer and not
> cobbling something together from mail-order parts.  All OEMs provide
> warranties and have varying levels of turnaround time for replacement.
>  You select the time you need based on the needs of the server,
> usually down to 4 hours.  If you need it faster than 4 hours, you can
> buy a cold spare at the same time you purchase the server.

Unfortunately, not everyone has a big budget.  Our friend Greg doesn't
seem to have the money to add a RAID card to his configuration.

> If you don't have the budget for that, software RAID works OK too,
> depending on the application.  I would also only use software RAID at
> levels 0 or 1 -- not on anything that requires a parity calculation
> like RAID5.  You probably shouldn't be using RAID5 these days anyway.
> 

I hear people say this all the time, I don't think they realize just
how fast a modern processor can compute RAID parity.  My laptop here
does RAID 6 parity calculations at over 3.5 gigabytes per second per
core. General purpose CPUs have been more than to compute RAID parity
for a very long time.

In the days before PCIe, I might have argued that it would be a good
idea to use a hardware RAID card for for RAID 10.  The Hardware card
would only require half the I/O bandwidth over the bus.  It was
extremely easy to max out the 133 MB/s bandwidth of the PCI bus.  PCI-X
was an improvement, but it takes a whole lot of drives to max out
PCIe.  Probably more than you can physically attach to a single
controller, unless they're SSDs.

I am definitely on Michael's side of with regard to software RAID.
Linux's software RAID is much more flexible and you can move the drives
to any random machine.  That alone is worth more to me than the cost of
any RAID card.

I have no knowledge of the current state of software RAID on Windows.
My knowledge in that area is about as old as Windows 2000 Server.

Pat