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Does Total Available Volume Size Increase AFTER Resync on Vertical Expansion?
I previously had 4x6TB in my ReadyNAS Ultra 4 on v6.10.4 & XRAID which gave me right about 16TB of usable space.
I switched to 2x6TB and 2X12TB (WD Red Plus) and performed a factory reset (with XRAID currently showing RAID5) to ensure all drives would be formatted and included under a single volume. I expected to see around 21TB of usable space.
The volume is currently resyncing (expected); however, the volume is only showing 16.3TB of usable space.
Shall I expect the volume to increase to the expected usable 21TB once resync is complete?
Bob_K wrote:
I switched to 2x6TB and 2X12TB (WD Red Plus) and performed a factory reset (with XRAID currently showing RAID5) to ensure all drives would be formatted and included under a single volume. I expected to see around 21TB of usable space.
The volume is currently resyncing (expected); however, the volume is only showing 16.3TB of usable space.
Shall I expect the volume to increase to the expected usable 21TB once resync is complete?
Short answer: yes.
Longer answer:
One thing to keep in mind is that the NAS reports space in TiB (1024*1024*1024*1024 bytes), not TB (1000*1000*1000*1000 bytes). Google will convert these units for you (try entering 18 TB in TiB in the search field in Chrome).
The capacity rule for single redundancy RAID is "sum the disks and subtract the largest". So 4x6 TB would give you 18 TB, which is ~16.3 TiB. Applying the capacity rule to 2x6TB + 2x12TB, we get 24 TB - which is ~21.8 TiB.
Your volume will be made up of two different RAID groups. The first RAID group is 4x6TB RAID-5 - which spans all disks, and has 18TB of space just like you had before. The second RAID group is 2x6TB RAID-1 - and fills the "extra" space in the two 12 TB disks. That will have 6 TB of capacity. The system concatenates those two groups into a single volume.
That second RAID group hasn't been formed yet - the first RAID group is still being synced. Once that completes, the second RAID group will be created and synced, and the capacity will increase to the full 24 TB.
2 Replies
Bob_K wrote:
I switched to 2x6TB and 2X12TB (WD Red Plus) and performed a factory reset (with XRAID currently showing RAID5) to ensure all drives would be formatted and included under a single volume. I expected to see around 21TB of usable space.
The volume is currently resyncing (expected); however, the volume is only showing 16.3TB of usable space.
Shall I expect the volume to increase to the expected usable 21TB once resync is complete?
Short answer: yes.
Longer answer:
One thing to keep in mind is that the NAS reports space in TiB (1024*1024*1024*1024 bytes), not TB (1000*1000*1000*1000 bytes). Google will convert these units for you (try entering 18 TB in TiB in the search field in Chrome).
The capacity rule for single redundancy RAID is "sum the disks and subtract the largest". So 4x6 TB would give you 18 TB, which is ~16.3 TiB. Applying the capacity rule to 2x6TB + 2x12TB, we get 24 TB - which is ~21.8 TiB.
Your volume will be made up of two different RAID groups. The first RAID group is 4x6TB RAID-5 - which spans all disks, and has 18TB of space just like you had before. The second RAID group is 2x6TB RAID-1 - and fills the "extra" space in the two 12 TB disks. That will have 6 TB of capacity. The system concatenates those two groups into a single volume.
That second RAID group hasn't been formed yet - the first RAID group is still being synced. Once that completes, the second RAID group will be created and synced, and the capacity will increase to the full 24 TB.
Thank you. I observed exactly that. The capacity stay at 16.36TB until the first RAID resync'd. Then it switched to 21.81TB and began resyncing (switching from "100% complete" to "50.47% complete") the second RAID. Ugh, another agonizing 21-hour wait until I hammer it with data! (Yes, I know I can use it now. I just prefer to wait.)
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