SGI Drive Sleds

What is a drive sled?

SGI sold many of its original systems to the military, who wanted to have drives removed and locked up at night for security reasons. So that this could be done easily, SGI implemented a very clever little system: The drive sled. It's basically a couple of guide rails, a plug and a latch that makes it very easy to slide drives in and out of your system. You hook up the drive to the sled once, and then you don't have to mess with its delicate cables anymore; you just plug in the sled. (One of these days I'll have to take a picture of one and put it here. In the mean time, here's some ASCII art)


---------------------|
                ~~~~~| < Power cable
                     |
 Ribbon ------> ~~~~~|:
 Cable          ~~~~~|:  < Nice big plug
                     |: 
---------------------|  < Rail
The drive goes in the big gap between the rails. If it's the huge 5.25" drive for which the sleds were designed, the ribbon cable has to be scrunched up quite a bit for the drive to fit: 


---------------------|
-------------------~~| 
|  Really big     |  |
|  huge old       |~~|:  < Look at how scrunched that ribbon
|  drive          |~~|:    cable is (see above illustration for
-------------------  |:    actual length)
---------------------|
You might actually have more success using a 3.5" drive, as I eventually did, although this requires some shims: 


---------------------|
   shim            ~~| 
   ---------         |
   cute little       |
   drive    ~~~~~~~~~|:  < Now the ribbon cable has a little more
   ---------~~~~~~~~~|:    breathing space and is strained less
   shim              |:    
---------------------|
On my system, with my specific drive sled, this was the only configuration that would work. But remember, you need to make a shim so that the drive will fit in properly.

The nice thing about drive sleds is that if you have multiple SGI machines, you can easily move drives between machines, since you only need to hook them up once. However, they can also hurt, mainly because they're expensive and hard to find.

You need a drive sled for each drive compartment you're going to use on your SGI. So if you have a main disk, a CD ROM and a tape drive, and you want to mount them internally, you need three sleds. A sled will be included with each device already mounted in your SGI system; however, if you are buying an extra drive, be sure to try and get it with either a sled or an external enclosure.

Greg Douglas of Reputable Systems has Personal Iris drive sleds for sale at $ 100 each, and Indigo drive sleds for $ 150. Reputable seems to be the best vendor for things like this and SGI-compatible CD ROMs. Greg has also been more than helpful in trying to get my system up; I endorse him unreservedly.

Since you can get an external enclosure for about $ 50, you may find it rather uneconomic to go the drive sled route. On the other hand, the system's definitely neater looking with everything centralized in one spot. And the amazing cooling system on my PI certainly cries for more drives. :-)

What other kinds of problems can you expect with them?

As we discussed before, The drive sleds have a small length of ribbon cable, which reaches out to the drive and connects all the crucial electronics. The cable is short and often has to be bent over to accomodate the position of the drive plug. This and all the scrunching you have to do to fit the drive in with the cable is very hard on ribbon cables, and as a result they are a frequent point of failure.

You can sometimes at least temporarily fix a drive sled cable by straightening it out and doing as little bending and twisting as possible.

Here's the one that really hurt.

When I installed my 3.5" drive, I discovered it was getting hot, because I didn't have the skins (the plastic casing on the side) installed. I decided to temporarily put the drive in the sled my CD ROM was using, so it would get better cooling.

Sometime when I was doing that, I dropped a screw. Somehow it lodged between two parts of the circuit board. When I put the drive in and turned on the machine I smelled a funny smell, and the drive got very hot. I took it out and discovered the screw.

Moral of the story: Be sure to look for and find every screw you drop during your installation. Otherwise you may do what I did and damage your drive. Apparently it's fixable by just replacing the circuit board, and at this point I'm just hoping it's not too expensive. :-(

The SGI Drive Sled FAQ has been accessed times since it was created on 08:45 14 July 1996. Wow!