that's not true. transferring a large amount of data in a consistent manner can be difficult. dumping your database without taking down your live site (or seriously impacting performance) can also be difficult without a dedicated backup slave. and the same can hold for any storage solution where you are short on IOs, no matter if the data fits on a drive or not.
I dunno, dude. This doesn't seem like a high that requires extremely high availability.
And anyway, if they can deal with rebuilding a RAID after a failed drive then (by definition) the site can deal with copying all the data off the drive. Heck, you could periodically yank a drive our of the RAID and replace it with a fresh one, and you'd have a backup.
Just yanking RAID drives isn't a way to guarantee DB consistency, especially if it's RAID5.
Database backups almost universally have to be made by the database system. This is no excuse for lacking a backup system; backing up databases is a solved problem.
Seems pretty clear that it's RAID 1 (mirroring). And isn't that exactly what RAID guarantees in a mirroring setup? That the two drives will have the same bits?
Even RAID1 doesn't guarantee this'll work. There are many ways simply disconnecting the secondary drive while cause problems:
1) The app may be in the middle of a series of DB commands that all need to complete with success before the DB is consistent at the app layer.
2) The DB is in the process of writing out some table rows and hasn't finished.
3) The DB has written some temporary locks to portions of the database that need to be released.
4) The OS hasn't committed writes from the DB to disk
5) The disk hasn't committed writes from the os to platter yet.
Your best bet of this working is to cleanly shut down your app, then cleanly shut down your DB and run an fs sync. After all that it might be ok to yank the drive.
Just yanking a RAID1 drive may work sometimes, but I wouldn't count on it. Especially when every DB system I know of has some sort of backup/dump mechanism. As someone else mentioned, RAID is great for providing high availability, but it does not provide disaster recovery.
With any sane storage subsystem you can un-mirror and re-silver hot. Lots of people used to back up Oracle like this (using a 3 way mirror), so you'd only be in hotbackup mode for a minute. This was before RMAN.
