Red Hat has, with good consideration and foresight, been pushing people to use logical volume management for a while. It's not completely integrated into the RHEL5 installer, but they're pushing hard to make it ubiquitous, and telling people this is the right way to do things. Unfortunately, the syntax for specifying logical volumes within DOS-style partitions is still a bit obscure, and the manual page examples don't show the LV syntax; this is fixable, but will take time.

I used software RAID and LVM on my new installation, but it doesn't boot -- I've found several articles on making GRUB work with software RAID, so I believe I'll be able to get it working. The docs say I should be able to just use "lvm" (which is present) to get an lvm shell, but neither lvm nor lvm.static does anything -- they just dump me back in bash.

Fortunately, "linux rescue" finds my partitions (this time), but not being able to even list out physical volumes is worrisome.

I want mirrored /boot, but it's RHEL's mirrored /boot capabilities are pretty limited:

If you are making a RAID partition of /boot/, you must choose RAID level 1, and it must use one of the first two drives (IDE first, SCSI second). If you are not creating a seperate RAID partition of /boot/, and you are making a RAID partition for the root file system (/), it must be RAID level 1 and must use one of the first two drives (IDE first, SCSI second).

Speaking of LVM being immature, check out What is the process to fsck lvm volumes? in the Red Hat Knowledgebase:

First, boot into rescue mode by using the correct media. This is very important: When prompted to mounted the drives, do not. Using fsck on a mounted filesystem will destroy all the data on that file system. This is unrecoverable. The data will be gone forever--save for very expensive hardware-level data recovery.