Yup all servers come in different depths, Units or U is just the height.
Most rack rails are adjustable so if you are using more than 1 type of chassis / manufacturer you will need to choose something which will suit all of your systems.
The main two are 800mm or 900mm, the latter of which suit most Dell + HP machines.
Most rack rails are adjustable so if you are using more than 1 type of chassis / manufacturer you will need to choose something which will suit all of your systems.
The main two are 800mm or 900mm, the latter of which suit most Dell + HP machines.