We use HP-UX and RHEL here. Yes, they're different enough from one another that there is a learning curve. AIX isn't so different from HP-UX, but RHEL is a different animal altogether.

The O'Reilly animal books are a good way to learn.

A few quick RHEL transition notes:
- While the LVM is an integral part of any HP-UX or AIX system, it is optional on RHEL. We're not using LVM on any of our RHEL servers.
- /etc/sysconfig/ is where a lot of OS config files can be found
- Google "selinux" it's a security layer that will cause you some frustration if you aren't aware that it's running and what it does.
- system-config-firewall-tui will let you open services for the software firewall.
- yum is the command to install and remove software. yum check-update to check for new updates, and yum update to install them. Software installation and updates occurs through "repos", the config files of which are found in /etc/yum.repos.d/
- mdadm controls the software RAID functionality, RAID-1 mirroring for your OS, for example. This is a different layer entirely from LVM. If you have a commodity server with a hardware RAID controller, you can ignore mdadm.
- If you opted to install the GUI, you can do user management, some system config, and other things via gui apps.

---------- Post updated at 01:23 PM ---------- Previous update was at 01:15 PM ----------

Yes you can fdisk and manually create partitions and filesystems (just like Microsoft Windows does). But nowadays, Linux has a robust and full featured LVM, just like HP-UX and AIX. It also has a high performance software RAID layer, if you're running on a machine without a hardware RAID controller. It also has strong AES256 volume encryption.

Any of these features can operate on a filesystem, a partition, or a full disk, and you can layer these features however you see fit, and it's all matured to enterprise level reliability.

Its come a long ways since 12 years ago.

---------- Post updated at 01:29 PM ---------- Previous update was at 01:23 PM ----------

Not necessarily. Linux LVM, mdadm software RAID, and cryptsetup disk encryption can all operate on whole disks. No partitioning required. And the kernel as well as the grub boot loader have the smarts to boot from them.

Of course you can still do manual fdisk partitioning, as with dos/windows days, and some folks (including myself) still do this out of habit and comfort zone, but it is no longer required.