Fortunately, server vendors offer external drive chassis to complement their servers. Most rackmount servers also support hot-swappable PCI cards. Some servers require you go into the management software and power-down the PCI slot while others let you pull out the cards. Hot-swappable PCI slots let you remove, replace or add cards without taking down the server. It's important to ask the vendor directly or to specifically look for this feature on the spec sheet.
Power supplies are also hot-swappable.
Generally, servers come with two hot-swappable power supplies and can accommodate three or four more. When equipped with more than one power supply, most servers can load-balance between them. More Than Internal Affairs Aside from the internals of the server, consider the design. Note how the server mounts in the rack and what the server is made of. Rackmount servers use significantly less plastic than towers.