Dell Precision 7920 Rack Owner's Manual

Rack Rails

The rail offerings consist of two types of rails — sliding and static.

The sliding rails allow the system to be fully extended out of the rack for service. They are available with or without the optional cable management arm (CMA).

Sliding rails with optional CMA

The static rails support a wider variety of racks than the sliding rails. However, they do not support serviceability in the rack and are thus not compatible with the CMA.

Static rails

One key factor in selecting the proper rails is identifying the type of rack in which they will be installed. Both the sliding rails and the static rails support tool-less mounting in 19”wide, EIA-310-E-compliant square hole and unthreaded round hole 4-post racks. Both also support tooled mounting in threaded hole 4-post racks, but only the static rails, as the more universal solution, support mounting in 2-post (Telco) racks.

The table below shows the sliding and static rail configurations and supported racks:

Table 1. Sliding and Static RailsSliding and Static Rails
Rail identifier	Mounting interface	Rail type	Supported rack types
			4-Post			2-Post
			Square	Round	Thread	Flush	Center
B6	Ready Rails II	Sliding	√	√	√	X	X
B4	Ready Rails	Static	√	√	√	√	√

NOTE:Screws are not included in either kit due to the fact that threaded racks are offered with a variety of thread designations. Users must therefore provide their own screws when mounting the rails in threaded racks.

NOTE:Screw head diameter for the sliding rails must be 10 mm or less.

Other key factors governing proper rail selection include the following:

Spacing between the front and rear mounting flanges of the rack
Type and location of any equipment mounted in the back of the rack such as power distribution units (PDUs)
Overall depth of the rack

The static rails offer a greater adjustability range and a smaller overall mounting footprint than the sliding rails. This is because of their reduced complexity and lack of need for CMA support.

Table 2. Static Rails AdjustabilityThe table below shows the flexibility of the static rails according to rail types.
Rail Identifier	Rail Type	Rail Adjustable Range (mm)						Rail Depth (mm)
		Square		Round		Threaded		without CMA	with CMA
		Min	Max	Min	Max	Min	Max	without CMA	with CMA
B6	Sliding	676	868	662	861	676	883	714	845
B4	Static	608	879	594	872	604	890	622	N/A

Note that the adjustment range of the rails is a function of the type of rack in which they are being mounted. The Min/Max values listed above represent the allowable distance between the front and rear mounting flanges in the rack. Rail depth without the CMA represents the minimum depth of the rail with the outer CMA brackets removed (if applicable) as measured from the front mounting flanges of the rack.

Cable management arm (CMA)

The optional cable management arm (CMA) organizes and secures the cords and cables exiting the back of the systems. It unfolds to allow the systems to extend out of the rack without having to detach the cables. Some key features of the CMA include:

Large U-shaped baskets to support dense cable loads
Open vent pattern for optimal airflow
Ability to be mounted on either side by simply swinging the spring-loaded brackets from one side to the other
Utilizes hook-and-loop straps rather than plastic tie wraps to eliminate the risk of cable damage during cycling
Includes a low-profile fixed tray to both support and retain the CMA in its fully closed position
Both the CMA and the tray mount without the use of tools via simple and intuitive snap-in designs

The CMA can be mounted to either side of the sliding rails without the use of tools or the need for conversion. However, it is recommended that it be mounted on the side opposite to the power supplies to allow easier access to the power supplies and rear hard drives (if applicable) for service or replacement.

Rack install

Rack Installation

Sliding rails

NOTE:The 2U system requires two people for installation due to its heavier weight.

Installing the system into the rack (option A: Drop-In)

The sliding rails are a "drop-in" design. This means that the system is installed vertically into the rails by inserting the standoffs on the sides of the system into the "J-slots" in the inner rail members with the rails in the fully extended position. As with all 2U systems, a minimum of two people are required in order to properly install the system in the rails.

Pull the inner rails out of the rack until they lock into place.
Figure 1. Pull out inner rail
Locate the rear rail standoff on each side of the system and lower them into the rear J-slots on the slide assemblies.
Rotate the system downward until all the rail standoffs are seated in the J-slots.
Figure 2. Rail standoffs seated in J-slots
Push the system inward until the lock levers click into place
Pull the blue slide release lock tabs forward on both rails and slide the system into the rack until the system is in the rack.
Figure 3. Slide system into the rack

Installing the system into the rack (option B: Stab-In)

The static rails are a "stab-in" design. This means that the inner (chassis) rail members must first be attached to the sides of the system and then inserted into the outer (cabinet) members installed in the rack.

Pull the intermediate rails out of the rack until they lock into place.
Release the inner rail lock by pulling forward on the white tabs and sliding the inner rail out of the intermediate rails.
Figure 4. Pull out the intermediate rail
Table 3. Rail componentRail component
Rail component
1 Intermediate rail
2 Inner rail
Attach the inner rails to the sides of the system by aligning the J-slots on the rail with the standoffs on the system and sliding forward on the system until they lock into place.
Figure 5. Attach the inner rails to the system
With the intermediate rails extended, install the system into the extended rails.
Figure 6. Install system into the extended rails
Pull the blue slide release lock tabs forward on both the rails ,and slide the system into the rack.
Figure 7. Slide system into the rack