So the HP RAID controller driver from around 2001 to ~2009 was the CCISS driver. There was a transition to the HPSA driver at some point, moving the Smart Array controller support back into the regular SCSI subsystem versus the dedicated block driver...
HP servers from the G1 to G5 era used the CCISS driver. On newer operating systems (EL6 and forward), HP ProLiant G6 and newer systems made use of the HPSA driver.
It turns out that RHEL7 removes the old CCISS module. Your fix in this case, since the Smart Array P400 controller in your G5 server isn't recognized, is to force the HPSA driver to load your older controller. Do this with:
As a module parameter...
From the man page.
hpsa_allow_any=1: This option allows the driver to attempt to operate
on any HP Smart Array hardware RAID controller, even if it is not
explicitly known to the driver. This allows newer hardware to work
with older drivers. Typically this is used to allow installation of
operating systems from media that predates the RAID controller,
though it may also be used to enable hpsa to drive older controllers
that would normally be handled by the cciss(4) driver. These older
boards have not been tested and are not supported with hpsa, and
cciss(4) should still be used for these.
This is a much more involved process than expected. You need to add that string to the module load parameters.
The official word is that the older controllers are just no longer supported. While you can get it running, it's less-than-ideal. So I'd probably stay away from EL7 for now. There will likely be a workaround, since there's an existing install base of these servers...
kernel component, BZ#1061210 When the hpsa_allow_any option is used,
the hpsa driver allows the use of PCI IDs that are not listed in the
driver's pci-id table. Thus, cards detected when this option is used,
are not supported in Red Hat Enterprise Linux 7.
kernel component, BZ#975791
The following cciss controllers are no longer supported:
◦ Smart Array 5300
◦ Smart Array 5i
◦ Smart Array 532
◦ Smart Array 5312
◦ Smart Array 641
◦ Smart Array 642
◦ Smart Array 6400
◦ Smart Array 6400 EM
◦ Smart Array 6i
◦ Smart Array P600
◦ Smart Array P800
◦ Smart Array P400
◦ Smart Array P400i
◦ Smart Array E200i
◦ Smart Array E200
◦ Smart Array E500
◦ Smart Array P700M