PowerEdge 2900 RAID array layout

my questions are parts and hard drive config related for a PowerEdge 2900 with the 8 hot swap SAS/SATA raid slots, plus the 2 drive flex bays also hot swappable on the same controller.  That much Im straight on.  The catch is, that Id like to use the floppy/tape slot above the left hand bay of 4 hot swaps, and the empty space above the right have 4 bays to put in an extra pair of mirrored drives running right off the MOBO.  Does Dell have an accessory avail to do that, or do have have to rig something so theyre not flopping around in there.  Just looking for a bracket of some kind.  That's the easy question, if anyone knows.  
 
2nd question  I want to run Server 2008 on it, with multiple virtual machines inside.  Probably a pair of SBS 03 and/or 08 machines. The current drive config is 2x 15k 36GB SAS mirrored and 3x 146GB 10K SAS RAID 5. Im adding drives and want to maximize power/storage/speed/redundancy/value.  
 
My understanding is that Hyper V works best with the parent server on its own partition.  Then the child partitions should all be static for the best virtual SBS install.  Also, SBS LOVES to have 3 sets of drives  OS, Exchange logs, Exchange Databases.  Storage can go wherever.
 
Im weighing two options, and am open to any other suggestions, since this is such a wide open field of compromises.
 
A:  Add two more 15k 36GB drives for a 4 drive RAID 5 totaling ~100GB of super fast storage.  Probably use that for a single SBS 08 OS partition.  Add one more 146GB 10K drive for a total of ~450GB of 10K RAID 5 on 4 spindles.  Thats the two sets of 4 bay hot swaps.  Then add a pair of probably 1 or 1.5 TB SATA drives mirrored in the flex bays for storage/logs and a pair of 80 GB SATA mirrored in the spaces I asked about in the paragraphs above.  This would give wicked fast performance, but due to the size of the drives, Id be much more limited in storage, plus only one of the SBS installs could benefit from the 15K RAID due to the recommendation of static virtual partitions and 100 GB OS partition recommendation for SBS 08.  So, Im not crazy about this approach.  Plus the drives would be expensive.
 
B:  Parent Server 2008 runs on the mirrored 36 GB 15K drives.  Add one more 146GB SAS 10K drive for the 4 Drive RAID  450 GB for virtual OS partitions, very fast.  Add 4 7200 RPM 1 TB or larger drives for mega storage in 4 drive RAID 5.  Also would add another two 1 TB drives in a mirror in the two spare slots above the hot swaps.  That would maximize storage, minimize cost, and would be pretty sweet.
 
 
Questions:  Does the parent server require the speed of 15K SAS drives?  What size would the virtual machines be? (assuming two virtual machines in Hyper V.)  Would 36 GB be adequate?  Would another arrangement make more sense?  Perhaps leave the 146 GB drives in 3 RAID 5 setup, and add another 3 drive raid 5 of X size, plus another mirror, those are the hot swaps, then add another Mirror above?  Im not sure what to try to do here, and there are so many options, its a little hard to decide.

Thanks
scottbly1Asked:
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OriNetworksCommented:
Just to give you an idea performance wise, I have a HyperV server running on RAID 5 Array(3 15K SAS Drives) which also hosts 3 virtual machines doin some basic web serving and printer sharing. I have another RAID 5 array(3 15K SAS Drives) on an additional controller running exchange 2007 with all roles. With my configuration, HD performance is pretty much maxed out. The exchange server is the only one running on that array but it also runs email AV and antispam, etc with about 50 mailboxes.

I may not be much help to the exact question but I just wanted to give you a real world example performance wise.
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scottbly1Author Commented:
yeah, that sounds like it's about as fast as you can get, barring a 4 drive raid the same way.  What kind of performance do you experience with it?  and what is your proc/mem configuration?
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OriNetworksCommented:
Well the physical host itself has 2 quad core E5335 xeons@2.0GHz and 12 GB RAM.

1st Array - %Disk TIme= 13
Physical Host Server 2008 Standard
Sharepoint (MOSS 2007) - 4 virtual processors - 4 GB RAM
CPU Light Use Avg. 10%-30%
Printserver (Printer sharing and custom web app, Symantec Management Server) - 2 virtual processors - 1.5 GB RAM
CPU Light Use Avg. 5%-10%

2nd Array - %Disk TIme= 30% Now, Normally around 60%
Exchange (Exchange 2007 all roles, AV, AntiSpyware, etc.) - 4 virtual processors - 4 GB RAM
CPU Light Use Avg. 5%-30%
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scottbly1Author Commented:
So, I understand there are some misleading elements to the processor % time when dealing with RAIDs.  I don't recall exactly off the top of my head what those were, but it has to do with the way the RAID drives are working together as one.  I stumbled across it while researching a raid performance issue on another server, that turned out to eventually be caused by a drive failing, but not reporting any smart status.

In any case, assuming that the % time is accurate, along the lines of CPU usage for disk exercise/available free time, that still leaves the question of PERCEIVED performance.  Your system sounds VERY similar to mine, except that i'm on 3 GHz processors.  What does the system feel like -- how is the exchange performance, etc?  this is my first venture into virtual systems outside of parallels, etc on a mac laptop.  I'm just about to start ordering drives, and if I can avoid laying the cash down for SAS, then I will.  I think this system will work much better for me with the space provided by Barracuda ES 1 TB drives in RAID 5.  They're enterprise Seagate drives on SATA rather than SAS, but with the correct time out times, etc, for RAID.  And cheap online.  So, what is your feeling about the server the way you have it set up?  Gigabit ethernet for access, i would presume?
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OriNetworksCommented:
Gigabit of course. Email flow has no noticeable delay except at high traffic times between early morning and mid day where is would only take maybe 5-10 seconds to get the email between accounts. We do get hit with tons of spam that gets filtered out which plays a part. With the multiple servers on the one array performance is perfectly fine, no delays ever.
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