Having problem with P410i smart array controller

This is several questions in one, so I'll try to address a few of them.

I typically set Smart Array controllers to leverage a higher write cache ratio. I prefer to have 75% write cache because the OS (using the XFS filesystem) caches aggressively. XFS will make a difference, but what are you tuning for? Are you tuning to simply achieve specific numbers, or is there an application requirement driving this?

ext3 isn't the fastest filesystem out there. But you have some mount options (e.g. noatime) and journal settings you could tweak.
I don't use LVM, especially with HP controllers that can provide many of the same benefits.
You have I/O scheduler and elevator settings (e.g. noop or deadline, in this case) that can be tuned, but that's a function of your application's actual needs.

If you do go with XFS, try a basic config then try some advanced configuration settings. Over time, I've ended up with mount parameters very similar to the one in the original link.

I just ran the following iozone command line on an XFS partition contained within a DL380 G5 with P400i, 12GB RAM and 8 x 146GB 10k drives. The elevator is set to deadline:

Command line used: iozone -t1 -i0 -i1 -i2 -r1m -s24g

initial writers  =  348957.75 KB/sec
rewriters        =  335130.03 KB/sec
readers          =  132851.70 KB/sec
re-readers       =  137116.27 KB/sec
random readers   =   35774.41 KB/sec
random writers   =  250618.38 KB/sec

Absolutely. Just pop in the HP SmartCD and walk through the RAID setup. If the disk is found, you simply add it into the existing array....reboot....done!