So, right now I've got 12TB of storage which contains about 8TB of data in my existing non-unraid HTPC. The drive capacities map out as follows:

 

1x3TB

4X2TB

1x1TB

 

I'm looking to switch to unraid for my storage requirements, but I'm trying to wrap my head around how many new HDDs I'm going to need to buy for the transition.

 

Correct me if I'm wrong, but as I understand it I can't just slap my existing drives into a machine running unraid and expect things to just work - I'll need a parity drive, (and I want a cache drive) and to get my existing data onto the unraid server I'll need to put fresh/blank/blankable drives in, let unraid prep them, and then start copying data over, then as drives get 'freed up' they can be added to the array.

 

What I'm getting at is: how many additional drives will I need to get started with the process?

I went through the same conundrum.  If time is no issue (and this will take a long time!), you need 1-3tb(N) and a 500gb(N) cache drive.  Realize your data will not be protected through the process.  This the least amount of new hardware I can think of.

 

Start by pre-clearing the new 3tb(N).  Add to the array.  Copy the data from your existing 3tb(1) to the array.  Off line, delete the data off the existing 3tb(1) then copy data from one of your 2Tb(1) to it. 

 

Pre clear the 2tb(1) you just copied over, add to the array. Copy data from the next 2tb(2) into the array.  Pre clear 2tb(2), add to the array.  Copy 2tb(3) into the array.  Preclear 2tb(3), add to the array. Copy 2tb(4) into the array.  Preclear 2tb(4), add to the array. Now copy the data from 3tb(1) into the array. Copy data from 1tb(1) into the array.  At this point, all your data should be on the 11tb storage in the array.  Pre clear the 1tb(1) and add to the array.

 

At this point, you should have 12tb of storage, 8gb data unprotected.

 

Now pre clear 3tb(1) and 500gb (N) for you parity and cache.  Add to the array, start a parity build.

 

You should end with 12tb of protected data storage:

Parity: 3tb

Data:

1-3tb

4-2tb

1-1tb

Cache: 1-500gb

 

Good luck.

I think I followed all of that, although I think you'll agree it's bound to be a bit of a twisty process. 

 

Thanks very much for the tip!

Honestly..

 

I feel the minimum # of drives would be 2x drives to purchase.

2x 3TB or 4TB drives.

 

Preclear both both drives and create a 2 drive array 1 parity and data drive.

migrate your existing 3TB drives data over (use terracopy or beyond compare)..

once you feel the data is migrated, good, copies and stable.. Preclear the existing 3TB drive and add it to the array.

Follow the same steps as above.for the rest of the drives.

 

it will probably take a week or more.  take your time if your data is important..

I also recommend you start with a protected array. since you will be erasing your old data, there will be no going back if something goes wrong. I just bought a new Hitachi 3TB drive the other day. it precleared 3 passes, went into my array, worked for 4 days then failed on first reboot. if it was not parity protected, I would have lost all my data on it. I see to many posts where a migration bad on non-protected arrays.

 

in the end, you will ended up with your 11TB and an extra 3TB for 14TB of storage. I assume you don't want a totally filled array from the start.

 

You could also start with 3x 2TB drives if that is better for your budget. create a 3 drive array with 1 parity and  2 drives for 4TB of data. When you migrate your 3TB, you just replace the temporary 2TB parity drive with the 3TB drive. this would still give you 14TB.

 

If you start out with 3x 3tb.. it would go a lot faster because you could migrate and preclear at the same time..

migrate your 3tb, then preclear it. while that's preclearing, start migrating a 2TB.

this is probably not so important when migrating 6 drives. for larger migrations, I would recommend it.

Hi - Just for info i did something similar to this not very long ago. I would go with the advice to create a parity protected array - i did not and suffered as a consequence. Its slower but with copies overnight etc it is much safer. Be safe, not sorry like i was.