[K12OSN] New Server Capacity Thoughts.

"Terrell Prudé Jr." microman at cmosnetworks.com
Mon Jun 9 00:31:11 UTC 2008

Almquist Burke wrote:
> On Jun 8, 2008, at 4:33 PM, Terrell Prudé Jr. wrote:
> > Can you clarify "can't control how the drives will be put to use"? 
> I use hardware RAID all the time, and I can control exactly how my
> drives will be used.
> He means that if you are using hardware RAID it actually sees the two
> drives as a single drive. You can't partition some of the drive as
> RAID 1, some as RAID 0, and some as just a standard partition. Also,
> you can't move them to a machine with a different RAID controller
> usually and still read them.

Hmm...I'm not sure why that would be desirable outside of an academic
exercise...but I guess if you're testing, it might be fun to play around
with.  I just don't see it as enough of a compelling advantage over the
benefits of hardware RAID, though.

And as for moving the drives to a different RAID controller, actually
that can be done if both controllers are the same model, often even the
same brand (I've done this with Compaq SmartArray 3200's to 5300's). 
This works because the RAID ID is stored on the drive as well as the
controller; the original purpose of this is so you can replace the
controller and not lose your RAID if said controller goes Tango
Uniform.  This is why my district tends to standardize on one or two
hardware platforms and then keep a spare RAID controller around.

I just put the OS (/boot, /, /usr, swap, etc.) on a RAID 1, and then
/home on a nice, big, honkin' RAID 5 with at least six spindles.  Great
performance that way, and good SATA disks are cheap.  You want to expand
your volume group with another RAID?  Much easier with hardware RAID's
"one disk" appearance to the OS than software RAID.

The point about swap, though, is a valid one, so I simply add enough
DRAM to where it isn't a problem anymore.  :-)  That's, of course, what
should be done anyway if swapping becomes an issue.


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