RAID Mirroring is among the most frequently deployed webserver disk configurations because it helps to keep machines running even after drive failure. It works by having two drives in a system, with the 2nd being an exact mirror copy of the first. Should the primary fail, the 2nd drive takes over and the machine can, in theory, continue to operate without so much as a hiccup. Add to the mix hot-swap drives that can be replaced without a shutdown and you have a very solid High-Availability solution.
If you’re running your webserver on a shared hosting account or VPS you probably already have disk mirroring without evening knowing it. But is it a backup strategy? The answer is unequivocally no, as one site, JournalSpace.Com, has painfully learned today. RAID Mirroring fails as a backup strategy because it isn’t a backup strategy at all: everything that happens to the first disk happens to the 2nd drive: do something stupid, like drop a database or delete all your files and guess what happens?
There can be no substitute for a comprehensive backup strategy – one that incorporates multiple off-site copies of the data – and these backups must never be overwritten. Don’t become a cautionary tale: performing backups is cheap; not performing them, as JournalSpace and their users have learned, can be suicide.