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Planning Ahead for Capacity Upgrade
Well, the ol' 4TB based volume in my 516 is down below 3TB free space. FWIW, this somehow got created as a RAID-5 under X-RAID2, but with 4TB disks it wasn't so bad. After some thought and looking at...
The volume will only expand when redundant space can be added. So if you have one 12TB disk after the RAID-6 volume is rebuilt you will still have dual-redundancy.
After you've created the RAID-6 volume you can re-enable X-RAID.
In fact depending what disks are installed, with a RAID-5 volume with three or more disks you could disable X-RAID and designate it so that when the next empty slot is filled it is used to add parity (i.e. convert to RAID-6). This conversion does take a long time though.
btaroli wrote:
Funny how complicated something so simple can be.
It would be nice if Netgear had an upgrade planning tool app built into the NAS - showing you what would happen on your specific system if you upgrade or add disks. I added that to the idea exchange here: https://community.netgear.com/t5/Idea-Exchange-for-ReadyNAS/Capacity-Planning-App/idi-p/1180068#M728
btaroli wrote:
P.S. It would be really nice if someday we evolved this situation to something more like ZFS or Btrfs, which don't stripe disks at all...
FWIW I don't think you are using the term "stripes" correctly above. Striping generally means the finer-grained organization of data+parity blocks. A RAID array of equal sized disks is still striped. I usually use the term "layer" where you are using "stripe" - though there might be a better term for it. That is, with XRAID2, mdadm is creating multiple raid layers (each with its own set of partitions) and is assembling them into a single volume. Each layer has its own raid striping.
Another aside - dual-redundancy could potentially be achieved if there are 3 disks of the largest size, but Netgear has chosen not to do it. You'd use triple RAID-1 for the uppermost RAID layer.
I agree long term that there could be a lot of benefits to integrating parity blocks into the file system itself. From a performance perspective, RAID resync now syncs everything, even free space. Why protect the free space?. Also, the newer schemes under development could potentially let you set different levels of protection for different files - allowing you to reduce or eliminate protection on data that doesn't need it, and increase protection on data that is more precious to you. Metadata could also be protected at a higher level, reducing the chance of file system corruption.
I think it will take some time before this approach will be production ready though.
Yes, I was being a bit loose with "stripe" but hopefully it's enough to get the idea across anyway. :) I'll check out that suggestion you posted. I think that would be awesome, and help avoid potentially nasty surprises for us users. :D
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