Linux MD? Or an H710p?

[Steve Bergman <sbergman27@gmail.com>]

Hello,

I'm configuring a PowerEdge R520 that I'll be installing RHEL 6.4 on 
next month. (Actually, Scientific Linux 6.4) I'll be upgrading to RHEL 
(SL) 7 when it's available, which is looking like it might default to XFS.

This will be a 6 drive RAID10 set up for ~100 Gnome (freenx) desktop 
users and a virtual Windows 2008 Server guest running MS-SQL, so there 
is plenty of opportunity for i/o parallelism. This seems a good fit for XFS.

My preference would be to use Linux MD RAID10. But the Dell configurator 
seems strongly inclined to force me towards hardware RAID.

My choices would be to get a PERC H310 controller that I don't need, 
plus a SAS controller that the drives would actually connect to, and use 
Linux md. Or I can go with a PERC H710p w/1GB NV cache running hardware 
RAID10. (Dell says their RAID cards have to function as RAID 
controllers, and cannot act as simple SAS controllers.)

I also have a choice between 600GB 15k drives and 600GB 10k "HYB CARR" 
drives, which I take to be 2.5" hybrid SSD/Rotational drives in a 3.5" 
mounting adapter.

Any comments on any of this? This is a bit fancier than what I usually 
configure. And I'm not sure what the performance and operational 
differences would be. I know that I'm familiar with Linux's software 
RAID tools. And I know I like the way I can replace a drive and have it 
sync up transparently in the background while the server is operational. 
I don't yet know if I can do that with the H710p card. I also like how I 
just *know* that XFS if configuring stride, etc. properly with MD. With 
the H710p, I don't know what, if anything, the card is telling the OS 
about the underlying RAID configuration. I also just plain like MD.

I like the 1GB NV cache I get if I go hardware RAID, which I don't get 
with the simple SAS controller. (I could turn off barriers.) I also like 
the fact that it seems a more standard Dell configuration. (They won't 
even connect the drives to the SAS controller at the factory.)

Any general guidance would be appreciated. We'll probably be keeping 
this server for 7 years, and it's pretty important to us. So I'm really 
wanting to get this right.

Thanks,
Steve Bergman