[dzeanah]

User of both QNAP devices and one of the iX systems devices here.

ZFS is sexy, but it requires planning and understanding and (as stated by another poster) adding storage in pairs of drives if you want to increase storage incrementally and maintain drive redundancy.

One of the perks of something like a QNAP or a Synology is the support for simply adding a single new drive to an existing RAID5 or RAID6 array, and having the storage box add it transparently while data is migrated to the new, larger RAID array. You pop in another 10TB drive in your RAID6 array and you increase the size of the array 10TB as you'd expect.

Or, if you've finally outgrown your 6-bay device which is full of 3TB drives, you can replace the existing drives with 12TB drives, then once they've all been replaced increase the size of the array to match the new drive sizes. This is done while the device is running and serving data - no downtime, though things may slow down as you would expect during migration operations.

From an end-user perspective this is a very different experience. Yes, FreeNAS/TrueNAS is cool, but I put a Synology at my dad's house.

[hestefisk]

The scenario you mention can easily be done with ZFS as well. I run a raidz1 and recently migrated from 3x4TB drives to 3x10TB. I bought one drive at a time and gradually expanded the pool. For each new drive I added I simply had to resilver the pool and I was done.