[ale] Onboard RAID

[Michael B. Trausch]

On 11/16/2011 01:20 PM, Greg Clifton wrote:
> OK folks, put down your flame throwers, but we're building a Windows
> 2008 server w/ mirrored boot drives and 4 2TB drives for data in a RAID
> 10 configuration for a customer. Modern motherboards give you the option
> of running Intel Matrix RAID or Adaptec RAID in the BIOS and I assume
> you can also run Windows total software RAID. So my question for the ALE
> brain trust is which is the better/best option and why so (and no
> running a Linux server is NOT an option in this case)?

Regardless of the operating system you are using, these days you want to
use some form of pure software RAID over hardware RAID (or "fakeraid",
that is, BIOS-provided software RAID).  The reason is that software RAID
layouts are more portable (for example, one can use Windows Dynamic
Disks even on Linux systems because the Linux kernel understands the
format used on them).

Given the power and bandwidth provided inside of today's modern systems,
you should not see any problems with doing RAID entirely in software,
and in the event of catastrophic failure the fact that the format is
well-known and understood makes it easier to effect recovery if ever it
became necessary.  (Of course, it never should, but things happen in
this crazy world...)

If you will always have an up-to-date backup system, then it doesn't
matter; offload to a hardware RAID controller if you have one as it will
save bandwidth on the computer's buses, but know that recovering the
data from the drives may one day be impossible, and if you have any
sizable window between successful backup run and complete array failure,
you might well be hosed in such a situation.

Ideally, you would separate that component out.  You can use those same
drives in some other box.  For example, you could have a small Linux box
that uses Linux software RAID, and simply expose the RAID device to a
dedicated network interface via iSCSI.  Then Windows 2008 can use that
iSCSI device for its own storage.  You get both upsides, then: bandwidth
savings (Windows isn't worrying about issuing writes multiple times, for
example) and a well-understood disk format for the RAID array's metadata
and data layout.  Plus, it leaves you options for later: for example,
you could use LVM to put two disks together, and use RAID to mirror
that, such that now you would have the space to perform block-snapshots
if needed, e.g., for backup purposes (which means you don't have to
worry about using Microsoft's heavy backup program to perform the backup).

	--- Mike

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