You most certainly can add drives to a zfs pool to expand it.
I've been running zfs on my file servers for ~17 years, have expanded the pool many times. In all that time I've only built a new machine once. Currently still running on my 2009 file server build. I've swapped and added drives to it over the years though.
You can add drives to a ZFS pool, but you need to either replace or add them in massive chunks (or smaller chunks if you're happy buying 2x as many disks as you actually need).
If I want one disk redundancy.
Today I can afford 2 10 TB disks.
Next year I need more than 10 TB capacity and I can afford one more disk.
Two years from now I need another 10 TB capacity and I can afford one more disk.
How can I perform this migration with ZFS? Going from 10 TB - 20 TB - 30 TB of capacity, adding one disk at a time, without losing redundancy.
Or say next year and two years from now 12 TB drives are cheaper. So with (10TB+10TB) + (12TB) + (12TB), Synology will give me 32 TB of usable space and I will have one drive redundancy throughout the whole time.
Honestly curious, this is a real-life situation that me and several of my friends have done with Synology NAS. For this use case, I would love to use cheaper and more performant used hardware, and not have to rely on proprietary software that phones home. ZFS requires upgrading your disks all at once, unRAID has single-disk performance, straight-up Linux BTRFS is "unstable".
> Honestly curious, this is a real-life situation that me and several of my friends have done with Synology NAS.
I guess I don't understand why optimize for the cost of a single drive, above all criteria?
Between this and the other comments, you've mentioned that Synology is over-priced, lower quality, lower performance, proprietary and phones home. Are you really better off vs. building a higher-quality more performant lower-cost ZFS server that's fully open source and has better reliability?
If Synology is higher cost, maybe take that difference in price to buy an extra drive or two?
To me a NAS is all about reliability.
> and I will have one drive redundancy throughout the whole time
Mentioned in the other comment, but that's not a good way of looking at it. What matters is the probability of loss of data while rebuilding the data after one drive has died. The more drives you have in that set, the larger the probability of loss. Your risk is increasing with every drive you add.
If you're comfortable with the large and ever increasing risk of loss (by adding drives without adding redundancy) then Synology is probably indeed a better match for your use case then ZFS.
I don't really understand why pay for dedicated NAS hardware if reliability isn't priority #1, but that's me.
Personally, for stuff that I care about but not quite that much, I just keep on the SSD on my laptop. It'll very probably be fine but there is risk of loss (same as Synology).
For the things I care deeply about, they go on the ZFS server with tons of redundancy, snapshots and backups. I'd never trust the truly precious data to anything other than ZFS.
> You most certainly can add drives to a zfs pool to expand it.
You can't replace drives with bigger ones and expand the pool. This is important, if you have 4/5/6/8 bay chasis and exactly the same amount of drives in the pool.
You can, although you need to replace all the drives in the pool. You can swap one, wait for resilver (or for a month, if you're in a budget), do the next one... And once you replaced every drive, you do like this:
I've been running zfs on my file servers for ~17 years, have expanded the pool many times. In all that time I've only built a new machine once. Currently still running on my 2009 file server build. I've swapped and added drives to it over the years though.