There are as many RAID types as there are technicians who set them up. RAID 1, RAID 10, RAID 5, RAID 50, RAID 6, each one of those with different parity schemes, stripe sizes, along with drive aggregate. All of these configurations will normally have some thought behind them as to their use in a certain environment. RAID 0 is good for situations where data access speed is paramount. RAID 1 is good for creating a hot swap situation in a real time environment. I have used RAID 1 when I was working with law enforcement 911 centers to ensure that the system would always be online.
RAID 5, the bread and butter of RAID configurations is the single most fault tolerant of all the RAID configurations and is used in excess of ninety percent of the time. That being said, RAID 5 will allow you to pull data off if you lose a drive, allow you to stay online for a limited amount of time if a project needs to finish, and RAID 5 will allow some limited hot swap capabilities. What RAID 5 is not, is a backup system and the following is the main reason why.
When a RAID 5 Data Recovery is needed, by dropping a drive there are many reasons for that, however, the most prevalent is that the drive has either a bad or slow read, or a bad or slow write. The drive is dropped from the array and considered degraded. At this time it is extremely wise to backup all of your data, bring the array down, replace the drive, bring the RAID back up and do a rebuild without anyone accessing the RAID. That’s the wise thing. What normally happens is that the RAID continues to run without a backup being performed and the RAID now becomes the de-facto backup. The problem now is that you have already had one drive fail, then chances of another failing very soon after the first are extremely high and it is only a matter of time before another one drops out and now the RAID is down.
RAID 5 is not a backup, it is a safeguard for IT professionals to get all data backed up before RAID maintenance is performed.