The 5TB plan is typically $59.12 for the first year ($79.50 per year thereafter), or $119.25 for the first two years ($159 thereafter). Acronis True Image is the only other service I tested that offers full NAS-backup support, while CrashPlan for Small Business does for Mac and Linux only. IDrive also backs up external hard drives and network-attached-storage (NAS) devices.
I like to have unlimited storage, but even 5TB will be enough for most users' storage needs. The IDrive Personal subscription plan comes with 5TB or 10TB of storage, depending on price, and can be used across as many computers, smartphones and tablets as you like.
