Soapm said: View Post
My "NAS" is a headless Debian server with a 12tb RAID (4x4tb in a RAID 5 array), would I need that much external storage to back it up?

You only need to have enough capacity as external storage to back up what data you want to back up and if it compresses then even better. So if you have 6 TB of data in use on the server as data you will need at least 6TB uncompressed data storage on external backup.

As you are not probably running RAID 0 where the total amount of disk space across all volumes is aggregated into a single array you probably have some mirroring / striping so your max data would be around say 6 TB of which typically you at a guess would be using around 3 TB so a 4TB external USB passport size USB drive would be fine.

Format the drive as a Linux one (mkfs.xfs or whatever file system you use) and just mount the thing and run backup from the server.

Incidentally with Linux you are usually far better off in using Software RAID (MDADM) than rely on usually cheapish consumer hardware RAID cards. Good quality hardware RAID cards are not cheap at all --software RAID often outperforms typical HARDWARE RAID cards quite significantly. Don't forget to install package ntfs-3g if you want direct access via READ / WRITE of Windows NTFS formatted HDD's. If accessing via SAMBA then not necessary although I/O will be far slower than using Native Linux File systems on the Linux machine.

Actually if you are going to backup your NAS to external devices using RAID 0 speeds the thing up considerably (very considerably !!!!) and you don't waste any HDD space with mirroring etc -- however the risk is that if a disk in the array gives a problem you lose the lot --but if you've got backup you can re-build.

On your system that (RAID 0) would give you 16 TB of fast HDD useable space !!!! you could use 2 RAID 0 arrays of 2 X 4 TB each. Chances of 2 breaking are about zero with modern disks and if you have backups so what !!!!. Note also unlike Windows Linux MDADM RAID 0 allows you to aggregate HDD's with different capacities too.

Risk to reward ratio !!!!!!!