Can I just remove a disk from a live RAID 1 array?

It depends on your controller.

If it supports hot-swap, then yes. If not, then you might blow the controller and kill the whole array.

If you do take a drive out of the array (either while running or powered off) you will have a full rebuild to do once you put it back in which will take a while and degrade performance while it happens.

Testing your RAID setup like this is not a bad idea. Just make sure your backups are correct and up-to-date first just in case something goes wrong and the array doesn't survive the test.

Well, according to a simple search that server should have "Hot-plug 2.5" SAS" drives, so if that's the case, yes you should be able to pull drives out and put drives in while the machine is live. However, you need to double check your actual setup.

This is something that you should do not only to impress your boss, but more importantly, to demonstrate to yourself how it works. You'll want to pull a drive to make sure that the system stays alive, and to make sure that your hot spare kicks in immediately. It's also a good idea to watch the rebuild process and notice just how long it takes. Replace the "missing" drive with a different drive, and check that you can create and assign it as a hot spare. Then pull the other drive that was part of the original array and see if the machine stays alive and the new hot spare kicks in.

Another fun test is to remove the drives with the power off, and put them back in in a different order, then fire up the machine and see what the controller says.

It's important to do this stuff before the machine is in production so that you a) know that it actually works, and b) can write up a procedure. You might be surprised at just how often a particular RAID setup just doesn't work as expected.

Since you're new at this, you might also see what a pulled drive looks like if you plug it in to some other machine and try to get at the data. You might also experiment with different sized drives to get a handle on how the system deals with them.

Call me paranoid, but ideally you might also consider buying a few extra replicates of whatever drives you're going to use, and test each one before the system is in production. I've had lots of stupid issues with minor drive size differences between manufacturers, defective drives that took out entire SCSI channels when inserted, etc. Life is good if you've got a few spare drives that are identical to the drives you're using.

Yes, if they are hot swappable you can just pull one of the disk and things should keep working.That is how you would replace a failed disk.