Two pools better than one?

[mrgeeza]

Hi there

I have an 8 bay, 2u rack mount NAS that I’ve had now for sometime, but not yet kicked myself into gear and set things up.

I’ve had a search round the forum but couldn’t seem to find an answer to my question, probably not using the correct terminology.

For 8 drives is it better to create 2 storage pools of 4 drives rather than one big one? Obviously there will be pros and cons to both, but if you can think of anything important I might have overlooked, I’d be extremely greatful.

Currently my opinion is to have 2 pools with one mirroring the other. In my head I see this being a kind of backup/redundancy if one of the pools fail, understandably a true backup is something on a completely different device and in a completely different place, but for quick recovery could this be a start?

So my question is 1 or 2 pools, mirrored or not? Pros and Cons.

Thank you :)

Toby

 

[Chris Moore]

What I would suggest is that you do some research. Here are some links to point out the things you should know.

Slideshow explaining VDev, zpool, ZIL and L2ARC

https://forums.freenas.org/index.ph...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/


Terminology and Abbreviations Primer

https://forums.freenas.org/index.php?threads/terminology-and-abbreviations-primer.28174/


Why not to use RAID-5 or RAIDz1

https://www.zdnet.com/article/why-raid-5-stops-working-in-2009/


FreeNAS® Quick Hardware Guide

https://forums.freenas.org/index.php?resources/freenas®-quick-hardware-guide.7/


Hardware Recommendations Guide Rev 1e) 2017-05-06

https://forums.freenas.org/index.php?resources/hardware-recommendations-guide.12/


Proper Power Supply Sizing Guidance

https://forums.freenas.org/index.php?threads/proper-power-supply-sizing-guidance.38811/


Don't be afraid to be SAS-sy

https://forums.freenas.org/index.php?resources/don't-be-afraid-to-be-sas-sy.48/


ZFS RAID size and reliability calculator 2017-05-17

https://forums.freenas.org/index.php?resources/zfs-raid-size-and-reliability-calculator.49/

 

[Chris Moore]

With only eight drives, you should just have one pool.

You can use snapshots to protect against file deletion.

 

[m0nkey_]

What size disks do you have? 8-drive RAIDZ2 is not unheard of. Z2 allows for any two drives to fail. The other option is mirrored vdevs.

 

[Chris Moore]

If you are really paranoid, there is also RAIDz3 where you can have 3 drives fail and the pool is still available.

 

[mrgeeza]

Well I did have 8 x 3TB SAS drives but I returned them as after a previous thread, I was concerned that I jumped into things a bit quick and should see what other drives might be better suited. My unit does both SAS and SATA so ether is fine.

I think my main issue is that I was cutting corners due to cost without thinking about the whole project. I was going to start with 4 high capacity SATA drives, then add more in the future, but from what I’ve been reading, this doesn’t seem to be an option as once a pool is created you can’t add further drives to the pool. Unless I’m missing something?

Therefore I had ‘cheaped out’ and got 8 lower capacity drives. Which like I stated, I returned shortly after ordering.

 

[Linkman]

You can't add more drives to a vdev (yet...), but you can add vdevs to a pool.

 

[SweetAndLow]

You can't add more drives to a vdev (yet...), but you can add vdevs to a pool.

Yes this! You can extend a pool by adding vdevss. You cannot change a vdev though.

 

[HoneyBadger]

I was going to start with 4 high capacity SATA drives, then add more in the future, but from what I’ve been reading, this doesn’t seem to be an option as once a pool is created you can’t add further drives to the pool. Unless I’m missing something?

As others have pointed out, you did miss something. You arrange drives into vdevs and then combine vdevs to make a pool. So you can start with four drives in a pool, and then expand that pool by adding four more. Your existing data will not be "re-balanced" when you add the new drives, but you will gain the additional space.

As far as which type of vdev to choose, that depends on your risk tolerance, as well as the type of workload you'll be placing on your storage. If you plan to use mirrors, then you can easily start with "two pairs of two" and expand by twos later. If you plan to use RAIDZ2, I'd actually argue that saving up and buying eight drives from the start is best, because you'll then be able to make an 8-drive Z2 and gain the usable capacity of six (versus getting 2-of-4, and then 4-of-8 later)

Can you post the exact hardware details about your "8-bay 2U NAS" such as CPU, motherboard, and crucially the HBA/SAS connectivity?

 

[pro lamer]

From the top of my head (I haven't seen your other threads)

If you want a temporary backup and are familiar with CLI you may consider building a striped mirrors pool (RAID 10 equivalent IIRC) and use zfs split command. More in this thread: https://forums.freenas.org/index.ph...-detaching-a-drive-to-a-mirrored-array.50687/

Sent from my phone

 

[Chris Moore]

Currently my opinion is to have 2 pools with one mirroring the other. In my head I see this being a kind of backup/redundancy if one of the pools fail, understandably a true backup is something on a completely different device and in a completely different place, but for quick recovery could this be a start?

Did you get a better understanding of storage pools? You would want to have a single pool and select the level of redundancy you want.
Do you have more questions?