Western Digital Internal Hard Drives: 4TB Blue PC HDD $59, 4TB Red Plus NAS HDD Expired

RAID is not a backup. The point of these NAS devices with multiple drives for redundancy is that if a drive dies, the NAS still works and your data is still accessible. Instead of you being stuck until you can replace the dead drive and restore from a backup, you can continue working. Order a new drive, and when it arrives you swap it in for the dead one and rebuild the NAS array.

RAID on a NAS does not constitute a backup because if you accidentally erase or overwrite a file on it, or ransomware encrypts it, it's gone. So even if you have a NAS, you still need to make backups of it.

So if your GF needs 100% uptime for this data, then a NAS is what you want. If her data storage needs exceed what's commonly available from a single external drive, then a NAS is what you want. If she needs to access the same data/files from multiple computers/devices in the house, then a NAS is probably a good choice.

But if she just needs a big drive on which to dump her data, which is already being backed up elsewhere, it's not time-critical if the drive dies (e.g. she can get another copy of the data from the school), and she only needs to access it from a single computer, then a big external hard drive will be cheaper, faster, smaller, and simpler.

Most people use a NAS in redundancy mode (RAID), so that it'll keep working if a single drive dies. In that case 2x8TB drives = 8 TB of storage. (The storage is the number of drives minus 1, so 4 drives = 3 drives worth of storage.) But as I mentioned, don't think of it as a backup. Think of it as insurance against single drive failure.

It is also possible to use a NAS to glom a bunch of drives together into one virtual drive. So 2x8TB = 16 TB. Just be aware that if you do that and one of the drives dies, in most cases all your data is gone. And if she needs to do this but she's the only one who's going to use the storage, then a RAID enclosure will probably be cheaper than a NAS. With a NAS you're paying extra for a small computer inside to present the HDDs over the network. A RAID enclosure typically just has cheaper RAID hardware to combine the drives into a virtual drive in a variety of ways, and usually attaches via USB like a single external drive.

Just as a heads-up, the 6TB model (WD60EFAX) is listed as incompatible with Synology boxen -- literally all of them.

Source: Their webpage. LINK [synology.com]

Reason: something-something-SMR

I'm sure someone will explain how you can just smear horse-paste on these and they'll work great, but if the data storing is for money, you'd likely want to know this in advance.

Just placed an order for three but questioning the wisdom of purchasing 4TB drives any longer. Yes, these drives are a bargain @$78 but considering the "price of real estate", i.e., the cost of a slot in your NAS/RAID, then 4TB is no longer a cost effective use of resources unless you repairing an existing array. I'm thinking that 8TB drive should be the minimum capacity for RAID5 configuration except the 8TB bare drives are currently inflated at $200+.