When I wrote Smart SOHOs Don't Do RAID almost two years ago, 500 GB was pretty much the max for single-drive NASes. But now that 1 and 2 TB single-drive NASes are here, even more home and small-office users can just say no to RAID solutions and opt for NAS-to-NAS backup.
Or can they? It turns out that NAS-to-NAS backup can become a frustrating exercise if you stray beyond the approach of using two of the same product (or product family). And even if you choose attached vs. networked drives for backup, your options with some products are less than optimal.
For example, Buffalo has supported scheduled backups of its NASes to attached USB drives since the original LinkStation and added scheduled backup, including encryption and compression, some time ago (Figure 1).
Figure 1: Buffalo LinkStation Pro XHL backup
But if you want to back up more than once a day, use a different vendor's NAS or even a plain old network share as the backup target, you're out of luck. Buffalo supports network backup only to other LinkStations or TeraStations.
Synology takes a few more steps toward flexible backup in that it supports networked backup to another Synology NAS or "rsync-compatible server" (Figure 2) and the option of (and built-in formatting for) FAT32 or ext3 formatted attached backups to both USB 2.0 and faster eSATA drives.
Figure 2: Synology Network Backup options
The catch with the rsync option is that you must supply a "Backup module" name as part of the configuration. Synology's documentation doesn't cover this, but a how-to in their wiki reveals that you need access to the rsyncd.conf file on the target rsync machine to obtain that information.
This is fine (well, sorta) if you're dealing with a Linux or Windows system running rsync where you have access to that file. But if you are trying to use another NAS, you're out of luck unless you can gain root access or find the information online.
The most flexible backup options, both networked and attached come with NETGEAR's ReadyNAS line, which has always supported scheduled backups to both attached and networked drives. The ReadyNAS' biggest claim to NAS backup fame is that it supports bi-directional backup via SMB/CIFS (any networked share), HTTP, FTP, NFS and rsync! (Figure 3)
Figure 3: NETGEAR ReadyNAS Backup options
It even differentiates among its USB ports and will back up to and from them. Backups can also be scheduled every 4, 6, 8, 12 or 24 hours.
But the ReadyNAS isn't perfect. Even the top-of-the-line ReadyNAS Pro doesn't have an eSATA port. So attached backups will be limited to relatively poky USB 2.0 speeds. And the networked backup options don't include compression or encryption; options that seem to be supported only by Buffalo.