External drive for backing up NAS -- USB3 vs eSATA

[sfx2000]

The reason I keep at it: as I understand it, one drive in a NAS backed up to an external drive -- that has to be be more fault tolerant than two drives in a NAS.

But people here seem to consider that an ill-advised solution, so I'm trying to understand if I'm missing something.

Obviously two mirrored drives in a NAS, which is also backed up to an external -- or two separate volumes in a NAS, which are backed up from one to the other, and then to an external -- obviously that's "even more" fault-tolerant -- but it costs three drives rather than two, and seems only marginally more fault-tolerant as compared to a single drive in a NAS backing up to an external drive.

I'm sorry if I seem thick or something -- but I'm genuinely confused why, for a two-drive solution, it doesn't make the most sense to have one drive in a NAS, and one external.

I'll take another stab at this...

A two disk NAS can be one of four general configuations...

1) RAID0 - the data is striped across the two disks - advantage, fast, disadvantage is that it's a single volume set that has twice the opportunity to fail

2) RAID1 - again, two disks, one is a master (let's call this disk0) and the other is a slave (let's call this disk1) - this is a mirrored set, any changes on disk0 will also occur on disk1 - advantage - data redundancy so if one of the two disks fail, the data is still on the other disk, disadvantage - the volume is half of the total of two disks, second disadvantage, is that either the disks are the same size, or if a size mismatch, the smaller disk will determine the size of the raid set

3) JBOD - this is a spanned volume across two disks, it's not raid, but the disks are managed together in a single logical volume - one can use different size disks, and have it span across both - not recommended for long term usage, IMHO...

4) two separate disks - they stand alone - this is the same as what one would have if just installing two discrete disks via ATA or USB

Now, all that being said - a NAS is not a backup, it can back up other machines on your network, but the wise comments here have, and I agree, strongly suggested that the NAS itself be backed up - whether theft, hardware failure, whatever, you need to have a long term backup strategy for that NAS box - and this is where the external USB device comes into play...

All of the major NAS vendors have software installed that allow the NAS to be backed up to somewhere else, whether another NAS, or to an external disk (either USB or in some cases eSATA). Not only just to back up the data, but some also offer the ability to back up the configuration files as well, so in the event of needing a restore, rolling the data back on, along with the configs, should allow the NAS to be placed back in service with less effort.

 

[stevech]

On 2) a significant disadvantage is also that anything wrong on 0ne disk is wrong on the other mirrored disk. Such as oops I deleted the wrong folder or some malware or file system corruption (power failure, NAS power supply/mainboard failure).