Not All Racks Were Created Equal
What is “Standard”?
In days past we had standards on a lot of items. If you wore a size 9 shoe, you bought a size 9 shoe. Not all size 9’s are the same anymore. We get the same thing in the Rack Solutions industry as well.
When dealing with server rack technical support, we hear the term “standard rack” all the time. A customer will come to us with “I don’t know why my 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 addressed:
- 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 threaded, 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, non-threaded 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 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 OEM’s slide rail and preventing the installation.
Again, the solution is often to find a third-party rail for the server or to use a fixed rail kit.
Problem #3 – Rear Door Collision
If we only had a dollar for every time we heard, “The server fits fine, except the back door of the rack won’t close”. This problem is caused by competition among the OEMs to fit as much technology as possible into a 1U or 2U server. They cannot make the box wider or taller, but they can make them deeper. And every year, the servers 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”).
- Sometimes the Cable management arms can be removed
- The back of the rail can be cut off
- Fixed rails can be used
- 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
For more information or to try and stump our experts, visit Rack Solutions