Probably the best definition of "highly available" is that you can do some math to get an estimate of your uptime. (99.8%, 99.999%, whatever. usually measured over a month or a year) And it's got to be a measurement of the availability of services to your customers; any measurement of "the server itself was up, it's not my fault the network was down" doesn't count.
This almost certainly means that you don't have any component requiring maintenance that brings down services when it gets a firmware update or something like that. Once you get past about 3 nines, it's likely your servers will have better availability than the network, your power, etc... (seems like there's vast swaths of the internet having problems for a few hours every few years, so you probably can't realistically get past 4 nines if the customers get to you over the internet)
As to what you described: it's a good start, and it depends.
The stuff that's prone to failure, in roughly the order of likelihood is:
- humans ("what's this button do?")
- software (sigh)
- anything with a moving part (hard drive, fan)
- chips (mostly because they have very small versions of the other electronics, and they have firmware which is software)
- capacitors (keep hearing about bad batches of these)
- transistors, resistors, other electronics especially if there's any kind of heat cycling
If the chassis, backplane, etc. in the RAID enclosure are fairly simple, they may be resilient enough to ensure 99.99% uptime (say, 4 hour repair time and 1 in 5 chance of a failure in a year) or something like that. That's likely better than your network or power availability, even with a couple network paths to your site and a reasonable UPS infrastructure.
It's possible that the RAID enclosure is really electronically two separate units with a separate path to each drive (dual-connector drives are common enough now), some kind of heartbeat between them and both systems connected to both controllers. If the non-redundant parts are simply a metal box and very simple wiring, that would qualify as "highly available" by most standards, since metal boxes don't generally fail and simple wiring is unlikely to fail unless it's made poorly.
In other words: we don't know. What's the MTBF rating and average repair time for each part?