Your Linux Data Center Experts

Unlike the Automatic Transfer Switch which I reviewed last week, the APC AP7900 and AP7930 I found to be much more satisfactory products. The AP7900 is a 1U 8-port and the AP7930 is a “Zero 0” 24-port remotely controlled power strip. By “Zero U” they mean that it mounts vertically to the side of the rack.

Unlike the ATS I previously reviewed, these actually did support SSH and SSL access. I was quite happy to find that. The down side of SSH and SSL is that the processor on these things is fairly slow, and initial boot-up when using SSH can take a lot of time. As in 5 to 10 minutes. It also takes a good 15 seconds to make a connection. There's also no way that I can see to set up SSH public keys for authentication, so you're stuck using password authentication.

Another drawback is that it only allows one user to be logged in, either to the web or SSH interfaces. So, if you are updating the outlet names and a computer needs to run a power-cycle, it will get a “Someone is already logged in” message until the other session logs out or times out.

This can be worked around by using SNMP to control the outlets, but that has another problem. It doesn't seem to be possible to restrict what outlets an SNMP “user” can control, so using SNMP means that a given machine can control ALL the outlets. In our situation, where we're hosting machines for many different users, we don't really want to give a particular user the authentication to control other users machines.

In the telnet interface (and presumably also SSH and HTTP) you can set up user accounts and give them access to particular ports, but that runs into the multiple login problem.

I really like that the boxes each have a LED display to show how many amps of power the attached gear is using. That makes it real obvious at a glance where you're at as far as circuit load goes. It's also extremely nice that they have everything on one side of the unit, including network and serial ports, the LEDs, and the power outlets, so you can flush mount it at the back. So many products seem to expect you to mount a front panel at the front of the rack, making it impossible to make the connections at the rear of the unit if you have servers above and below it, and only hard if you do not.

They also provide these bars you can mount to the units which allow you to zip-tie the power cords to the bar, preventing accidental unplugging. This is a fantastic idea for the products which do not use twist-lock outlets. Unfortunately, in our situation we won't be able to use the bars on the Zero-U units, at least initially, because it will interfere with the rack-mounting screws as we have to install them in our cabinets. I could imagine a better designed locking system that would use less space, but at least they provide something to help with accidental unplugs.

They also include power cables which are plenty long to connect the power switches to the up-stream power. In fact, they may be a bit overly long. They'll run the full length of a 7' rack, and then some. If you're using a lot of them, or don't have much excess space, the long cables might need to be trimmed and some new plugs put on.

These products are well thought out and well executed.

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