Backing up Hyper-V to an external hard disk using eSATA or USB 3 is an efficient way to protect your Hyper-V infrastructure.
As with all methods and strategies, there are advantages and disadvantages. USB drives have their own, too.
Hyper-V backup to external disks connected to a Hyper-V host is incredibly fast. A typical modern drive can easily each speeds of over 150MB/sec.
Naturally, restores from portable disks are even faster than backups, so in the case of a disaster recovery your Hyper-V VMs are quickly back on the host where you need them.
Another great advantage of using external hard disks is their low cost: 5TB are now (2015) available for just $130. That’s 2.5 cents per GB!
Backup rotation is another big advantage. Simply configure your disks in Windows Disk Management to use the same drive letter or use separate tasks for each drive.
A great advantage of BackupChain is that you can simply unplug and plug in the next drive and continue. Rotation doesn’t affect restores or backups. BackupChain stores everything on each disk separately.
There is no need to change backup configurations and all of your data can be restored from a single drive, no matter which.
Portability is a great advantage. You could simply take the drive and plug it into another Hyper-V host. If the VMs are stored uncompressed you could even boot directly from the portable disk and instantaneously recover the virtual machine in seconds.
USB disks still need to be locally attached and manually rotated.
External hard drives are, at some point in the future, going to be too small for the data load. They can’t be extended like a NAS, for example.
Portable disks are electrically connected to the host. If the host is damaged by a power surge, these drives are likely going to die with it. However, the backup drive rotation strategy protects you from this type of risk.
Some disks are prone to overheating. Buy a well ventilated device and place it away from heat, vibration, and sunlight.
Due to their small size, external backup hard drives may be accidentally dropped. You would want to handle them with care.
When transported, make sure they are not exposed to cold temperatures or temperature extremes as this may cause condensation
Backing up Hyper-V to external devices is what most SMBs today take advantage of. The era of expensive proprietary tape drives is coming to an end; however, there is a place for all technologies out there. The important thing is to know the pros and cons of each so you make the best choice depending on your situation.