Why All Racks Are Not Created Equal

Standard Rack?

When dealing with server rack technical support, you hear the term “standard rack” every day. A customer will say “I don’t know why by server won’t fit, I have a standard 19″ rack”. The problem lies in the fact that, although there is a document defining standardized 19″ racks, there are a lot of details left out of the specifications. The standard is EIA-310.

What the EIA-310 Rack Standard does not include

Here is a brief list of rack details not completely defined or address:

• Does the rack have 2 posts, 4 posts, or even 6 posts
• How deep is the rack’s mounting depth
• What is the thread type of the rack
• Are the rack holes thread, square, or round
• What is the shape of the rack upright: “L”, “C”, or “?”
• Are there obstructions between the front and rear posts
• How much space is between the front door and the front post
• How much space is between the rear door and the rear post

Problem #1 - Rack Holes

Rack hole type is the number one reason for server and rack incompatibility. This is why we always recommend square hole racks. You can always add threads with a cage nut if you need them. Most modern server rails are designed for square holes. Only a few OEM rails are compatible with both round and square holes.

As an example:

• Dell’s RapidRails only work in square holes.
• Dell’s VersaRails work in round unthreaded holes, but not threaded holes such as 10-32 or 12-24.
• Dell now has a combo rail that can switch between Rapid and Versa, but still does not work with threaded holes.

The solution here is often to find a third-party rail for the server or use a Fixed rail kit.

Problem #2 - Uprights and Obstructions

The second most common type of server and rack incompatibility is rack obstructions. The EIA spec does not address what the rack manufacturer does between the front and rear mounting posts. There are often additional flanges or other mounting features. These obstructions are notorious for colliding with the OEMs slide rail and prohibiting installation.

Again, the solution here is often to find a third-party rail for the server or use a Fixed rail kit.

Problem #3 - Rear Door Collision

If I only had a dollar for ever time I heard ” The server fits fine, except the back door of the rack wont close”. This problem is caused by the OEM competition to fit as much technology as the can into a 1U or 2U server. They cannot make the box wider or taller, but they can make them deeper. And every year the server get even deeper until racks can no longer hold them. In the 1990’s a 36″ deep rack worked great. In the early 2000’s a 39.37″ (1 meter) rack was the standard. Now racks are being sold as deep as 42″ and 44″ deep.

The solutions to this problem are limited, but there are a few (If only we had invented a “Rack Stretcher”) . Options include:

• Sometimes the Cable management arms can be removed
• The back of the rail can be cut off (we do this all the time for Dell 1950 and 2950)
• A Fixed rails can be used

More Information

• What is a 19″ Rack
• What is a Rack Unit (”U” or “RU”)
• What is EIA-310
• Wikipedia has an in-depth overview of 19″ racks.
• Why all racks are not created equal

This entry was posted on Tuesday, November 6th, 2007 at 10:01 am and is filed under 2 Post Racks, 4 Post Racks, Popular, Racks. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.