ADD VDEV or use what I have

[Temereen64]

Greetings Everyone,

I have a supermicro case with 24 drive bays. I currently have 12 of the 24 bays filled with 6TB and 8TB nas drives. I was thinking to set up Freenas on the initial twelve drives (2 VDevs of 6 drives with Raidz2). I thought initially that I would set it up and add two additional vdevs of 6 drives to the pool at a later point in time when finances permitted. After reading I realize now that by doing this, my data would be striped over the first 12drives and by adding 2 vdevs later only new data would be striped over all four vdevs. I wanted to add one more VDEV and had the following question:

1. I just purchased two more drives (Total of 14, 2 additional to create a third VDEV of 6) Both are 10 10Tb nas drives. Things are a bit tight now so I cannot purchase the other 10TB drives as of yet. I have the oppportunity to get some very cheap 1TB (Sata 2) datacenter drives that are used and have about 40,000 hours on them (Of course they would be run through smart test and badblocks before even considering adding them to the pool). I was thinking I could create a third VDEV by using the two 10 TB drives and adding 4 of these data center 1TB drives which would give me six drives in a third raid z2 VDEV. (Mixing the 10B and the 1TB into a third VDEV) Later when I get the additional drives I could remove the 1TB drives one by one and replace them with 10TB drives and allow them to resilver taking the capacity of the drives up to 10TB and allowing the third VDEV to be striped from the beginning. What do you all think? Would I run into issue by mixing SATA 2 and Sata 3 drives on the same VDEV/backplane? How would you all approach this? Should I do what I stated above? Would it be better to use what I have and wait until I get four more 10TB VDEVs and then set up the third VDEV? (It will be about 4 months until I can get four more 10TB drives, the 1TB drives would just be placeholders so to speak) I have about 10TB of data that I need to transfer to this server. (Note: I could also get 6 (10 total) additional 2TB (Sata 2) drives and fill up the fourth set of slots for a total of 24 and create a fourth VDEV.) again the datacenter drives would just be placeholders until I get the funds necessary to make the additional purchases on new drives.

Alternatively should I just take the 12Drives that I have, set up two VDEVs and get the pool going and increase it and add new VDEV's when I have the money for the additional 10TB drives and forget the 2tb Datacenter Drives altogether?

Thanks,

 

[Heracles]

I realize now that by doing this, my data would be striped over the first 12drives and by adding 2 vdevs later only new data would be striped over all four vdevs.

The reality is even worst than that : the new data will be highly concentrated on the new set of vDevs only, as long as needed until the usage on second set of vDev catches up with the first.

and allowing the third VDEV to be striped from the beginning.

Again, not completely correct : that vDev will be so small compared to the others, it will fill about the same rate in proportion, so will contain much less than one third of the data despite being one third of the vDev number.

From what you described, I would do :
--A first mirror with 2x 10TB
--A second mirror with 2x 8TB

That will give you 18TB, so filling it up with your data will push you up to about 50%.

When you are ready, create a new pool with a new set of mirrors and using all the drive you intend to use in the long run.

Once that new pool is ready, you migrate your data from your first pair of mirror to that pool. That way, data will be pretty well spreaded.

You then destroy your first pool, re-create the 2 mirrors and add these 2 in the new pool. Yes, these 2 will be empty, but in proportion, you will be pretty well distributed.

Should you wish to go for perfection, you can :
Do as explained for the first pool with 2 mirrors.
Create as many mirrors as you can for the second pool.
Degrade one 10 TB mirror in the new pool and the one in the first pool. Caution : you will loose redundancy from here.
Degrade one 8TB mirror in the new pool and the one in the first pool. You will be even more shaky.
Use these to create 2 more mirrors and add these in the second pool.

Then migrate your data to the new pool.
Once done, destroy the first pool and re-use the drives to re-silver the degraded vDev in the new pool.

Then you will recover redundancy and your distribution will be ideal.