Theoretical vDev and Hard Drive Replacement Scenario

[Mirfster]

Just a theoretical question...

Say I create an initial RaidZ2 with the following: 2 x 2TB Drives & 4 x 3TB Drives (Manually via GUI of course). Understanding that FreeNas will only allow me to use the 2TB of space for the 3TB drives.

So, for giggles, I decide that I want to re-allocate the 3TB drives and decide to replace each of them with 2TB drives. Is FreeNas going to give me problems if I try to replace a technically larger hard drive with a smaller one even though it is only permitting me to use 2TB?

I know I can do it the other way around, replacing the 2TB drives with 3TB drives; but am just curious...

 

[Mr_N]

as long as the 2TB drives your using are same exact size as the original ones and not smaller because of weirdness between different models/manufacturers then i dont see why not.

 

[Mirfster]

Was just about to update this with some test results..

Using "FreeNAS-9.3-STABLE-201602031011"

1. Created a "TestPool" using 1 RaidZ2 vdev of 6 drives
   • 4 x 3TB
   • 1 x 2 TB
   • 1 x 1.5 TB
2. Showed Total Space of 8.1 TiB (Raw) and 5.2 TiB (Usable)
3. Replaced a 3TB Drive with a 2TB Drive
   • No issues seen; Space remained the same
4. Then I Replaced the 1.5 TB drive with the 3TB Drive that was just Replaced
   • vDev is now 4 x 3TB and 2 x 2TB
   • Total Space increase to 10.9 TiB (Raw) and 7.0 TiB (Usable)

Only oddity I saw was that the "Compression Ratio" went from 1.00x to 8.25x? However, I am doing some other testing with this machine so I will re-run the scenario once more without the other stuff to be sure....

 

[Mirfster]

Update: Compression Ratio was not changed by this process. Will see what did cause it last time though..