TerraMaster Forum

this is more so just a general question and curiosity, i guess this can also be related to a NAS drives also

so i now have a 4 bay DAS, i have populated it with 2x 6TB drives, and configured it with TRAID (as its backed of a NAS drive)

i assume the idea is that if one drive goes down i can pop in another 6TB drive and it will rebuild the array (still with 2 drives) thus not losing any data

if i was to put in a 3rd 6TB and then one drive went down, would the rebuild take a shorter amount of time (it it can read half the data from one drive and half from the other) or longer because it has to manage 3 disks not 2?

or doesnt it affect it

Excellent question!
Since your D4-320 is connected to the TNAS and used with its array mode managed by the TNAS's TOS system (TRAID), regarding the rebuild efficiency for 2-disk vs. 3-disk configurations, the conclusion is: increasing to 3 disks does not speed up the rebuild process; it may actually slightly increase the rebuild time.

Here is the technical logic behind this:

1. 2-disk mode (logically equivalent to RAID 1)

• Rebuild method: linear mirror copying.

• Process: the system only needs to read data from the single surviving disk and write it intact to the newly replaced 6TB hard drive.

• Efficiency: this method is the simplest and most direct, with speed limited only by the physical read/write limits of a single hard drive.

2. 3-disk mode (logically equivalent to RAID 5)

• Rebuild method: parity reconstruction (XOR calculation).

• Process: the system cannot simply "read half and write half." It must read all corresponding data blocks from the remaining two healthy disks, perform XOR mathematical operations via the CPU to calculate the missing data, and then write it to the new disk.

• Efficiency: although RAID 5 may be faster during normal data reads, during rebuilds, the computational overhead and multi-disk synchronized seeking add extra burden. Therefore, managing a 3-disk array rebuild is usually slower than the mirror copy of a 2-disk array.

Operational suggestions:

• User Guide: How to Repair RAID?

• Ensure stability: during the rebuild process, please ensure stable power connections for both the NAS and the D4-320. Since the expansion enclosure communicates with the NAS via USB, it is recommended to avoid frequent large file transfers during the rebuild to reserve sufficient bandwidth for array synchronization.

• Intelligent sleep: although the D4-320 supports intelligent sleep, during array synchronization, the system will automatically keep the hard drives awake until the task is completed.

Just FYI, I just added another 12TB to my D4-320, it had 2 x 12TB (TRAID)
Oh yeah, it's a storage pool for the F6-424 it's attached to.
So, it basically went from RAID 1 to RAID 5, the add disk/rebuild took (I wasn't doing the math myself)
1 day, 14 hours, 45 minutes
2325 minutes
38 hours (rounded down)
The F6 was not used at all during this time, other than the occasional peek to see how far the process got.
Out of pure curiosity is it because of the RAID 1 --> RAID 5, meaning if I ever (with HDD prices as they are) add a 4th 12TB to the unit, should it take just as long.
I also understand "It is what it is"

For RAID configurations with redundancy, adding a new drive causes changes to the data striping structure. Therefore, this process requires reading all data and parity information from the existing drives, recalculating it, and writing it to all drives (including the new one).
This takes roughly as long as overwriting all drives one by one.