[kwlug-disc] Docker Host Appliance

[Ronald Barnes]

Chris Irwin via kwlug-disc wrote on 16/01/2023 14.45:

> But I'm a home user. And a cheap one, at that. I have a bunch of
> data and a bunch of disks, and I want to be reasonably sure both the
> data (and backups) are valid.

Then ZFS is the only option - only it detects (and can *correct*)
corrupt data (if I understand correctly).



> Back in the day I had 2 drives. Eventually I wanted to expand, so I 
> bought two more drives, and added them to the filesystem (was using 
> btrfs). Run a rebalance, it shifts data around, and I have a bunch 
> more storage capacity.
> 
> With ZFS, I don't think I can do that. I can't take my four drives, 
> and turn it into a six-drive array. I'd either have to build a whole
>  new larger array (vdev?) and migrate to that, then throw out the old
>  disks.

I'm not very knowledgeable about ZFS, but https://2.5admins.com/ podcast
has Allan Jude (a ZFS dev from Hamilton) and Jim Salter (former writer
for Ars Technica), also a ZFS enthusiast, and it's almost a meme about 
how often they work ZFS into conversations.

 From listening to them, as I understand it, you'd take the 2 new disks,
make a vdev from them, then add that vdev to your pool and storage space
has expanded.


Corrections to my understanding welcome!



> I've been using mdadm (+lvm) and btrfs for a lot of years,
I use mdadm + lvm myself, but only through inertia. Adding btrfs to that
is never gonna happen; as Doug pointed out, it's not reliable.

And with layers upon layers (ext4 on lvm on mdadm), it still doesn't
achieve the features of ZFS at a single layer.


And that's not even mentioning block-level snapshots, which I don't
think lvm supports?

Even rsync falls far short of ZFS's ability to detect a single changed
block in a 1TB file and backup only that one block.


> You can switch redundancy levels on the fly,

That's something I don't think ZFS can do.



> if you wanted. WIth BTRFS if I had four disks and one failed (and I 
> have enough free space), I could rebalance the array to use one fewer
> drive and recover a measure of redundancy while waiting for 
> stock/sale/shipping/payday.

Sounds like a handy feature.

But again, with btrfs RAID5/6 *should not be used in production*.



> ZFS also can't fully utilize mismatched disks, apparently. My
> 4-drive array has 2x6TB and 2x8TB drives, which means there's 2x2TB
> worth of unusable space on the 8TB drives. This worked fine with
> btrfs.

I believe you could have 1 vdev of 6TB drives and 1 vdev of the
8TB drives together in a pool without losing the 2GB.



Again, I'm no ZFS expert, but the above is my understanding and if any
of it's wrong, happy to be corrected.


Cheers!

rb