When I set up a server using one of the free unix based systems, I will usually configure them so that they will send an email message if there is a problem with the RAID system. Recently the server of a photographer client did send a message saying that one of the disks had a problem. I contacted the client and he replaced the disk, which was then added to the RAID array. A few weeks later I received a message saying that another drive had failed, so I contacted the client again so that this next drive could be replaced. This made me realise that the whole array could have gone, if the message sending system was not in place, so if you are running a server with a RAID on it, then you had better make sure that you also have a messaging system in place, so that you do not find it has disappeared one of these days. With "hardware" based RAIDs, you will have to install some software that can monitor it, but this software will usually be custom to the manufacturer, so it can be difficult to integrate it with another third party monitoring system and it might not also be configurable from the command line, which would make it a bit useless on a headless system. The RAID system on Centos is fully command line based, so it can be fully configured over SSH and it also has some other features which are critical for when it comes to data recovery.