Is it possible to create a system backup by creating a RAID 1 array
of 3 disks with 1 of the disks always not connected to the system?
Technically it is possible.
Now can we assume that disk 2 is a backup of the system?
Yes. HW tends to make full disk arrays.
So you have a full copy of half a mirror.
Every week, repeat swap and RAID rebuild.
Is this a recommended practice?
NO!
Why or why not?
Several reasons. For starters you are making a full copy every week. If you have a 4TB disk and one file changed then you are still copying the full 4TB. **Wastefull*
Secondly you are assiming that the rebuilding always works, and you are testing that assumption weekly. Not a practice I feel safe with. And if I needed to do that I would create a backup before trying this. In your case, that kind of defeats the purpose.
Thirdly: Swapping hardware weekly will wear things out. Even hotswap connectors are not designed to be changed hundred of times.
Now, as what to are best practices:
- Multiple partitions, one with the OS, one with data.
- A good backup of the OS. This probably does not need weekly backups.
- A $longer_period full backup of all data and $shorter_period of incrementals. (or an rsync like backup).
- And an off-site location for the backups.
The last because having a backup is nice, but if you store it on-site and there is a fire you will also loose the backups. Ditto for lighting strikes. And doubly so when either happens during a backup cycle.
And if you do use off-site backups then the data reduction from incremental backups gets double interesting.
Also note that RAID is not backup. RAID is great to keep a server up and running when a disk fails. Than after office hours IT can do emergency maintenance. It is never a replacement for a backup.
And if used at home then you still want backups which are safe from fire, lightning, theft, ...
