Is it possible (and safe) to mount a 19-inch 4u rack server on a 2-post rack... by only its ears?

  • You mean "wings"?
    – Andrew
    Jun 28, 2010 at 22:53
  • @Andrew: I've heard "ears", "tabs", "wings", and a small variety of other names. I think it's just a regional thing.
    – Chris S
    Jun 30, 2010 at 12:39
  • 17
    How would you like it if we held you up by your ears? Jun 30, 2010 at 13:14

11 Answers 11


Only if you don't have any problems replacing it after it falls. I wouldn't chance it.

  • 2
    +1. I agree whole heartedly.
    – joeqwerty
    Jun 28, 2010 at 23:01
  • 2
    And when it does go, there's a reasonable chance it'll damage the rack it's in, and anything else below it..
    – Dentrasi
    Jun 30, 2010 at 16:54

IMHO, No. Servers are meant to be installed on rails or shelves. The "ears" are meant to secure the server in the rack, not to support it.

  • Actually, this is true for most servers, but not all. Sun had some 1U servers that only had ears, not rails. (eg. Netra X1) Of course, they were also less than 2 foot deep, so didn't need to support as bad of a moment. I've never seen a 4U "server" that shipped like this, although I have seen some larger network gear (eg, most Xyplex terminal servers, Cisco switches, etc.)
    – Joe H.
    Jun 30, 2010 at 14:34
  • @Joe H: I agree. If the equipment doesn't span the full length of the rack (communications equipment typically) then it's usually mounted by the ears. Full length servers are another matter altogether.
    – joeqwerty
    Jun 30, 2010 at 14:55
  • 2
    I had some real short depth 4U servers back in the day that were designed to be ear-mounted. No rails/shelf necessary. Jun 30, 2010 at 17:07
  • most server rails only attach at the front though?
    – JamesRyan
    Jul 1, 2010 at 16:06
  • Not that I've seen. Most rails I've worked with attached at the front and rear.
    – joeqwerty
    Jul 2, 2010 at 0:07

Look at the server's manual. If you haven't bought it yet, look online -- there's normally a mounting guide of some sort, and it might have specific instruction for dealing with a two post rack.

Some systems have alternate holes tapped in the sides so you can mount the ears closer to the center of gravity. The system will stick out the front of the rack, but it'll cause less torque.

Other systems have enough of the heavy components far enough forward that they're fine with 2 post mounting with only sticking out a few inches. (basically, you turn the ears around before attaching them).

Another option is to get a shelf rated for the weight, and install that to take the load of the server.

  • 6
    +1 for the shelf - this is what I've done when I've absolutally had to rack mount a server in a 2-post rack (in an A/V cupboard). Shelves rated for that much weight usually cover several units to distribute the load evenly. Jun 28, 2010 at 22:40
  • I forgot to add one more option -- place it in the bottom of the rack, so it's supported by the base of the rack if it tries to rotate.
    – Joe H.
    Jun 29, 2010 at 11:46

I'm sure it is possible, but if it isn't designed to be mounted that way, then I wouldn't risk it.

  • I've seen some flimsy 2-post racks, my money would be on the rails bending out of shape, ripping out the screws that hold the rack rails in place (especially if it's in say an A/V cupboard where the racks may be mounted against veneered plywood or MDF) Jun 28, 2010 at 22:39

Is it possible? Yes

Is it advisable? No


Short answer:

It depends on your system. You need to find and read the racking manual, or contact the vendor.

Long answer:

Only if you don't have any problems replacing it and the systems underneath it after it falls, to borrow the quote from @PHLiGHT . If you're racking other hardware near this server, and you bump this chassis by accident, will it fall and crush your hands or toes? What if it fell partway and bent the rails? What will you do then?

For many rails, the weight is transferred from the server to the rails to the little screws holding it into the rack. With most servers this is fine, because you have two rails and 4 screws per rail. With a two post system, you might be looking at only two screws on each side of the 4U box. That sounds dangerous.

How are the ears attached to the side-rails? Are they attached with nice solid connections, or are they attached with little wimpy screws, or with little sheet-metal flanges?

  • 1
    Okay ... the civil engineer in me is compelling me to bring up an issue -- if you've properly installed the ears, the screws aren't taking the weight. The friction between the ears and the server is taking the sheer load; the screws are providing tension to create the friction, but taking very little of the sheer load (the weight in this case). The screws only take a significant load in this situation if they're not torqued down properly, or if there's a lateral load (eg, an earthquake)
    – Joe H.
    Jun 30, 2010 at 21:05
  • You might be right. And I Am Not A Civil Engineer, but I'm looking at several sets of ears right now, and I'm not convinced that the friction is holding everything together. Some of the ears do have flanges to hold the weight, but not all of them. Jul 1, 2010 at 18:30

Yes you can do this, but I wouldn't recommend it. some servers are very heavy and could also do with support at the back. If your server is only a 1U then it's not a good idea because it's likely to bend at the front.

If it's 4U case then there is generally enough strength at the front to support it OK. I've done this before when we didn't have rails.

Trouble is, it's a real pain to get at the server when things go wrong or you just need to pull it out for some reason. They can be very heavy as you know and when you remove the bolts the whole thing either drops or puts its full weight on the server below (which may be supported in the same way.

Get some rails if you can. Or if you can't get these then other option is to get a shelf and make the server sit on the that. At least then you can remove a couple of bolts and slide it out a bit on the shelf. You can even get shelves that slide.


Possible yes, albeit briefly. Safe, no.

If for some reason you really need to mount a server into a 2 post rack you MAY be able to get away with using cables attached to the top of the rack to support the rear of the server. While that will work it is clearly not the preferred option.


Those 2 post racks are usually called telcom or relay racks. Networking equipment is usually fine to put on them, but they are not designed for servers in general.


I actually have a heavy rackmounted server that miraculously survived having one of it's "ears" fail when it was being racked. They absolutely WILL bend and break. I say no. (I'll post a picture later)


I've recently had similar problem with this APC Smart-UPS, which is how I ran into this question.

This is the manual, which came with it.

The first step on the manual instructs to attach the two "ears" on the sides of the UPS. I assume the OP was asking whether a UPS can be mounted by those only. That sounds insane!

Instead, my problem was that the package came with 2 "slightly larger ears", which should be mounted on the front poles only (as shown on the manual). I was actually baffled even at this, and worried these could not hold the UPS. Instead, I've found some proper 4-pole rails, which I would have been much more comfortable with.

In the end, I was told I should stop worrying and love the "slightly larger ears". To my surprise they can indeed hold the weight, especially since the batteries are on the front of the device, and happen to be just the same depth as the "ears" extend. The drawback is I have to make sure not to ever put pressure on the back of the UPS accidentally.

PS. Some manufacturers have specific instructions to mount their storage servers by the ears. Still looks crazy!

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