Leseratte10 Posted February 6, 2022 Share Posted February 6, 2022 I have not yet set up my UnRAID machine (I'm just in the process of buying all the parts to build a new machine), so I apologize if this is already mentioned somewhere in the UnRAID UI, but I haven't found it being discussed on the forum anywhere. Right now, the parity drive(s) for UnRAID need to be the largest drives in the array, and if you try to add a new data drive that's larger than your parity drive, UnRAID won't let you do that. I do understand why that's needed - on a data drive that's larger than the parity drive, the storage at the "end" of the data disk wouldn't be protected by parity. But lets assume I have a setup with one 8TB parity drive and two 8TB data drives each, and the data drives are at capacity and I need additional storage NOW, as fast as possible. I run to the store and grab a new 12TB drive (or whatever size is currently cheapest in terms of $/TB), and then I would either need to throw away my parity and re-build it on the new 12TB drive (giving me three 8TB data drives and one 12TB parity drive), or I would need to migrate the parity data to the new drive. Both solutions are not ideal - the first one means my array is entirely unprotected until the parity is rebuilt and if a drive dies, I'm screwed. And the second solution means it's going to take a long time to copy / migrate the parity data, probably even with a long-ish downtime, and I cannot use the additional storage immediately - I would need to wait until the parity move is over. However, just by looking at the documentation about how UnRAID works, there should be a theoretical third solution, which I haven't found anything about online. I believe UnRAID currently doesn't support that, so that's why I'm writing this post. Assuming I have an array with 2x 8TB data and 1x 8TB parity - what if it was possible to add the new 12TB drive as an additional data drive, but have UnRAID limit all writes to that drive to the first 8TB? Create an xfs partition that's just 8TB and ignore the rest. That'd mean my new 12TB data drive would act like it was just an 8TB data drive, with the last 4TB unused / unavailable. But it would also mean I'd get an additional 8TB of usable storage *right now* without having to mess with parity. And then in the future I have all the time in the world to get yet another new 12TB drive, migrate the existing 8TB parity drive to a new 12TB parity drive, and at that point unRAID would recognize "Hey, the parity drive is now larger, that means I can now unlock/use the last 4TB on that data drive by resizing the file system". Basically, it would mean that you could *add* data drives to your array which are larger than your parity drive, but you'd only be able to use the same amount of space that your parity drive has. Am I missing something that makes this not work as I described? Or is this just not implemented in UnRAID for whatever reason? I'm not saying I absolutely need this feature, but it would be nice to be able to expand an array with a larger data disk, even if it means I cannot use 100% of it (until I get a larger parity drive). Quote Link to comment
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