I used to have big HDDs attached to my Thunderbolt dock.
But it was always annoying having to 'eject' them before unplugging the laptop from the dock. Or sometimes overnight they would disconnect themselves and fill up my screen with dozens of "you forgot to eject" notifications. Yes I'm on macOS.
Do NAS avoid this issue? Or you still have to mount/unmount?
Why does there seem to be much more market for NAS than for direct attached external HDD?
Eventually I got a new laptop with bigger SSD, started using BackBlaze for backups, and mostly stopped using the external HDDs.
I always assumed NAS would be slower and even more cumbersome to use. Is that not the case?
A NAS will use a network file protocol (SMB/NFS/AFP/SFTP etc) to access data rather than direct disk access, so the types of failures are different. Generally you don't really have to "eject" but disconnecting during a large transfer can cause incomplete writes.
The main risk with directly attached storage is that most kernels will do "buffered writes" where the data is written to memory before it's committed to disk. Yanking the drive before writes are synced properly will obviously cause data loss, so ejecting is always a good idea.
Generally, NAS is a bit safer for this type of storage because the protocols are built with the assumption that the network can and will be interrupted. As a result, things are a bit slower since you're dealing with network overhead. So, like everything, there are some trade-offs to be made.
> Why does there seem to be much more market for NAS than for direct attached external HDD?
I can access my NAS from anywhere in the world, but you can only access your direct-attached drives when sitting at your desk.
I can hide my NAS in a closet, but your direct attach drives are wasting valuable desk space and causing noise in your workspace.
My NAS has a software raid (raidz2) so any two of my drives could die without losing a single bit of data. Technically this is possible with direct attached drives too, but usually people aren't attaching multiple external drives to their computer at the same time.
Multiple people/computers/phones can access my NAS simultaneously, but your direct attach drives are only usable by a single computer at a time.
I can use my NAS from any device/operating system without worrying about filesystem compatibility. With direct attach drives, you need to pick a filesystem that will be supported by the devices you want to plug in to it.
The downside is a NAS is running 24/7 which will consume more electricity than drives you only plug in on-demand, and file transfers will be slower over a network than directly plugged in to your computer, but 99% of the time the speed difference does not matter to me. (It really only impacts me when doing full-disk backup/restore since I'd be transferring hundreds of gigabytes.)
You can configure a NAS to use Wake-on-LAN, so that it will not run 24/7, but only when you wake it up remotely. After you finish using it, you power it down remotely, until the next use.
You can disable this notification with
defaults write /Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist DADisableEjectNotification -bool YES