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Available space 8 bay with 3 drive sizes
Hi
I've been playing round with the Readynas Configurator.
I was looking at putting the following in - but there is some unsused space.
I can't see why - unless it's a x-raid limitation.
Shouldn't it create md127 over the first 6tb of all drives, then md126 over the next 2tb of the first 6 drives and then finally md125 with the final 2tb of the first two - enabling all space to be used??
I've certinaly had expanded arrays with md125/6/7 on them.
I know in effect the 10tb form the parity of the RAID6 array. Shouldn't it be showing about 2TB more??
(ie 2x10 parity - so space would be 8x4 + 6x2 = 44 then adjusted down to real space about 41-42TB)
What am I missing??
Thanks
A
Sandshark wrote:
RAID6 needs at l;east three drives,
Actually in the ReadyNAS it requires at least 4 drives. Triple RAID-1 would be a simpler option for dual redundancy with three drives - but the NAS wouldn't do that either.
Note that if you use the usual equations for P and Q here: https://igoro.com/archive/how-raid-6-dual-parity-calculation-works/ then RAID-6 with three drives has the same on-disk layout as triple RAID-1 (P and Q would both be equal to the original data block). So there's no reason to waste time with parity math or rotating data and parity blocks - you might as well just do triple mirroring.
powellandy1 wrote:
So why is all space not being used here (3x10tb, 4x8tb, 1x6tb)??
Each layer has at least 3 drives.
Because the NAS won't do RAID-6 with three drives.
Also, you'd need to install the drives in order of size. Assuming that was done, XRAID would have 8x6TB and 5x2TB RAID groups. Then there would be 2 TB on each of the 10 TB drives that couldn't be used.
However, the breakdown in the RAID calculator incorrectly states the volume size.
8x6TB -> 36 TB of capacity + 12 TB of redundancy
5x2TB -> 6TB of capacity and 4 TB of redundancy
3x2TB -> 6 TB of unused disk space.
Total capacity is 42 TB (~38.2 TiB) - not 41.7 TiB as stated in the calculator.
Total redundancy is 16 TB (~14.6 TiB)
Total unused is 6 TB (~5.46 TiB)
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RAID6 needs at l;east three drives, so the last 2Tb of the 10TB can't be used to create one. XRAID assumes you want at least as much redundancy on all layers. So while a RAID1 from only two drives creates similar redundancy (one drive) in a RAID5 configuration, it does not in RAID6.
Thanks
So why is all space not being used here (3x10tb, 4x8tb, 1x6tb)??
Each layer has at least 3 drives.
Sandshark wrote:
RAID6 needs at l;east three drives,
Actually in the ReadyNAS it requires at least 4 drives. Triple RAID-1 would be a simpler option for dual redundancy with three drives - but the NAS wouldn't do that either.
Note that if you use the usual equations for P and Q here: https://igoro.com/archive/how-raid-6-dual-parity-calculation-works/ then RAID-6 with three drives has the same on-disk layout as triple RAID-1 (P and Q would both be equal to the original data block). So there's no reason to waste time with parity math or rotating data and parity blocks - you might as well just do triple mirroring.
powellandy1 wrote:
So why is all space not being used here (3x10tb, 4x8tb, 1x6tb)??
Each layer has at least 3 drives.
Because the NAS won't do RAID-6 with three drives.
Also, you'd need to install the drives in order of size. Assuming that was done, XRAID would have 8x6TB and 5x2TB RAID groups. Then there would be 2 TB on each of the 10 TB drives that couldn't be used.
However, the breakdown in the RAID calculator incorrectly states the volume size.
8x6TB -> 36 TB of capacity + 12 TB of redundancy
5x2TB -> 6TB of capacity and 4 TB of redundancy
3x2TB -> 6 TB of unused disk space.
Total capacity is 42 TB (~38.2 TiB) - not 41.7 TiB as stated in the calculator.
Total redundancy is 16 TB (~14.6 TiB)
Total unused is 6 TB (~5.46 TiB)
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