[ale] Onboard RAID

[Michael B. Trausch]

On 11/18/2011 12:18 AM, Richard Bronosky wrote:
> Have you guys ever heard of the Killer Nic which runs Linux INSIDE the
> nic card so that gamers that have to run windows don't have to deal with
> the crappy MSFT network stack? How cool would it be if someone made a
> RAID card that ran Linux so that you can put the power of a Linux
> software RAID into a windows machine (for stupid customers/CTOs). You
> would have the benefit of knowing that if your RAID card dies and you
> cannot find a replacement, you will be able to use Linux software to
> recover your data. This _should_ have the added benefit of allowing you
> to move between cards and card vendors because they all will interface
> with the disk in a consistent manner.

That's more-or-less the basic idea in having a "appliance" type box be
your RAID box.  Actually, there are some RAID boxes on the market now
that actually use the Linux kernel's software RAID stack for
implementing their "hardware RAID", which is nice.  You get a box that
uses a standard, well-known on-disk representation and layout for the
metadata and payload itself, which to me is the most important thing.

Why?  Because odds are if you lose the array it's going to be 10 minutes
before your scheduled daily backup on a day where a major ton of work
was just done and/or sideloaded onto the array and there are no other
copies available.  Of course, Murphy may even go to the great trouble of
ensuring that every bit of data is gone that you need to recover in such
an instance, but thankfully he isn't always that mean.

The additional nice thing is that you can easily put the disks in
another system such that you can intentionally build a damaged array in
order to try to read data back off of it.  Or for that matter, since the
layout is documented in source, you can simply write some userspace
utility in a pinch to peel off as much data as you can get.

Point being, while there is no true standard format for the storage of
RAID data, the Linux kernel's implementation is about as close to de
facto standard as you're going to get in practice.  It's worth using
simply for that, if nothing else.  The fact that the more complex RAID
modes are more efficient in software is a consideration for me, too,
though I don't typically really worry about speed; even RAID 6 is fast
enough for most loads where it is used (unless a disk is down; then
reads slow way down).  But that's fine, too, if you ask me: that
provides an indicator that will cause my client's office to call me.
Though with the system I have in place, I will likely know that a drive
died before they do.

	--- Mike

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