1.3 KiB
1.3 KiB
+++ title = "So why do I need a backup?" description = "Because RAID protects you against one and only one specific thing: disk failures." weight = 2 type = "post" +++
Having a number of disks in RAID may seem like a backup, especially if you're using a mirror mode. But this is wrong!
RAID protects you against one and only one thing: a disk failure. It does not protect you against any of the following things:
- Multiple disk failures beyond the RAID level chosen (e.g. both disks in a mirror, or 3 disks in a RAID-6).
- Failure of the RAID controller itself (especially when using hardware RAID), the computer itself, or the environment (a flood, or fire, perhaps).
- Data corruption on-disk from filesystem bugs, cosmic rays, or minor hardware or firmware failures.
- Malicious or accidental deletion or modification of files by yourself or another party, including viruses, bad application writes, or administrative mistakes (e.g.
rming the wrong file ormkfson an existing filesystem).
Even ZFS, designed specifically to prevent the third point, is still susceptable to the others.
The adage is simple: "RAID replicates everything, even the stuff you don't want, like the deletion of that file you needed."
For these reasons and more, RAID IS NOT A BACKUP!