Am I even barking up the right tree?

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John M. Długosz

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I think ZFS is quite cool, but read through the documentation and I'm disappointed to see that the redundancy operates on a volume level rather than a per-object level. That is, it doesn't support a mismash of different sized disks and arbitrary adding of a disk, as I had thought (that is, unless each disk is a volume set of 1, which gives no redundancy).

Considering building a FreeNAS or similar appliance rather than "upgrading" my existing RAID5 for more capacity, mainly for future proofing against the next such need. I put "upgrade" in quotes because replacing three 1TB drives with larger ones is really a replacement, and I'd have to back up and restore existing data rather than grow-in-place. Adding another stripe of only 1TB more is not appealing since for the same power/noise I can get 3TB now.

So, suppose I start with a ZFS system (using FreeNAS) with 3 3TB drives to give 6TB of storage with redundancy. Now, a few years down the road I want to increase the capacity. Adding another redundant volume set to the pool would require adding 3 more drives at once (or, 2 more for mirroring but that's half the capacity for 2/3 the price). Replacing one drive in the existing set would not increase the capacity.

If I understand the writeup of Drobo, OTOH, it will use RAID across partitions rather than whole drives only, and automatically do a RAID5 with the size of the smallest drive, another RAID5 with one partition from each remaining drive, etc. until there are only two left in which case it does a RAID1. So, it uses almost all the storage of mixed-size drives (I don't know if it supports re-balancing when adding or replacing a drive, to what extent).

I could do something like that with a home-built system, if I don't mind taking the storage offline to rebalance after a major change.

But… I really like the ZFS. The guard against hidden data corruption, and the performance through caching is compelling.

So, how might I plan and use FreeNAS to accomplish my envisioned upgrade paths?

—John
 

survive

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Mr_N

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Well first forget raid5, it became not so redundant a while ago, so yeah adding 4 or 6 drive raidZ2 vdevs at a time is your best option
 
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