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 running the RAID, or the environment (a flood, fire, theft, etc.).
- 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.
rm-ing 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, instantly, even the stuff you don't want." Like the deletion of a file or corruption.
For these reasons and more, RAID IS NOT A BACKUP!