If RAID-1 is an exact mirror copy, why must you do a "rebuild" on a RAID-1 drive after the primary drive fails? Will the system suffer from any downtime if the primary drive fails?
Are there any hot-backup options RAID levels available that can withstand a drive failure without having to rebuild or suffer from any downtime?
You don't have to rebuild, you can run it in a "degraded" (just one disk) state.
But ofcourse, if the other drive fails too, you lose all your data - usually you have raid to prevent that, so there's no point in having raid with just one drive, and not rebuilding it.
You can have raid1 with three drives, so when one fails, you don't need to rebuild anything, since you still have raid1 with two drives... but if two disk fail, you still have one disk, and no redundancy again.
ps: raid is not(!) backup!
I think you're confused about the purpose of RAID. The rebuilding occurs after the replacement of a failed drive. Data from the healthy drive is copied to the new disk.
And our local RAID technology question: What are the different widely used RAID levels and when should I consider them?
