That's a tough one.  In the telco space, the common sizes are 19" and 23".  19" for gear, 23" for fiber patch panels, etc.  There are also some 25" floating around (Nortel, I'm looking at you). 

 

Unfortunately, 19" gear fits in 19" racks.  It fits in 23" sometimes -- if the manufacture makes both size ears, or you have to use an adapter plate, which can be a pain, and expensive (for 25" you may as well find a local machine shop to make them for you, or it's cheaper to remove them and start over). 

 

Sometimes you can do 19" gear and 23" cable management in a 23" rack, which is nice.  There is also the telco proclivity to attach stand-offs on the back side of the rack for vertical cabling, which can take up even more space.

 

The one thing you really can't do is take servers, etc. designed for a cabinet or 4-post style rack and put them in a 2-post neatly.  There's adapters and things, but they're a pain as well.  At least with a 4-post square-hole rack you can get 80% of what you want to fit.  


-----Original Message-----
From: "Coy Hile" <coy.hile@coyhile.com>
Sent: Monday, March 30, 2020 5:31pm
To: "Karsten Elfenbein" <karsten.elfenbein@gmail.com>
Cc: "NANOG" <nanog@nanog.org>
Subject: Re: rack rails



> On Mar 30, 2020, at 5:24 PM, Karsten Elfenbein <karsten.elfenbein@gmail.com> wrote:
>
> Hi,
>
> something like https://www.opencompute.org/projects/rack-and-power
> comes into my mind for that.
> Mounting on 4 posts should be the default. It is insane what some
> vendors want to mount on 2 posts only.
>

That brings up an interesting question. As I understand it, the penchant for two-post mounts come from what are at least colloquially termed telco racks that are or were common when you had tons of modem banks and such. Are such mounts — much like DC power — still quite common in the service provider space, or do most use more or less normal racks? (That said, the 750mm wide (29.5in) racks that actually have room for high density cables inside the rack seem much more useful for a networking application than the 600mm wide version.)



--
Coy Hile
coy.hile@coyhile.com