Creating a zfs pool with "room for near-future expansion"

[Andreaux]

Hi all,

I might be out of my mind, but I am planning a new NAS system but can't right away afford all the disks I plan on putting in. I had the idea then to create a degraded zfs pool accounting for the soon-to-be-purchased drives that I will replace the "fake" offline drives in the pool with.

So in short, I am planning to have an 8 x 6TB pool and I would like to start with 2 drives (which I can have now) and create an 8-drive pool with 6 offline drives and replace then bring them on as I can go with sourcing the new ones.

Is there any danger in using this newly created 2/8 pool until I can add further drives?

Sorry for the newbie question :)

Any help appreciated.

 

[Alecmascot]

Create a mirrored pair, then add more mirrored pairs as more drives become available.

 

[Chris Moore]

Reading for clarity:

The 'Hidden' Cost of Using ZFS for Your Home NAS
https://louwrentius.com/the-hidden-cost-of-using-zfs-for-your-home-nas.html

Slideshow explaining VDev, zpool, ZIL and L2ARC
https://www.ixsystems.com/community...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

Overview of ZFS Pools in FreeNAS from the iXsystems blog:
https://www.ixsystems.com/blog/zfs-pools-in-freenas/

Terminology and Abbreviations Primer
https://www.ixsystems.com/community/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/

 

[Chris Moore]

Is there any danger in using this newly created 2/8 pool until I can add further drives?

The idea you have will simply not work at all. You can create a RAIDz2 of six drives using smaller drives and replace the smaller drives with larger ones as the larger drives become available.

 

[Andreaux]

The idea you have will simply not work at all. You can create a RAIDz2 of six drives using smaller drives and replace the smaller drives with larger ones as the larger drives become available.

Why would it not work at all? I’ve seen it suggested here when someone wanted to transition from a 2-drive mirror to a 3-drive raidz1. My only concern is using the pool for weeks with a few drives offline.
The raid would start empty so there’s no legacy data to copy over.

 

[Andreaux]

Create a mirrored pair, then add more mirrored pairs as more drives become available.

I thought about this, but I’d like to have a raidz2 pool at the end.

 

[Alecmascot]

@Andreaux make sure you do a good write-up then we can see how it is done.......

 

[PhiloEpisteme]

I think @Alecmascot's suggestion is the best solution here.

Think of it this way as well. A FreeNAS server on its own should not be considered a backup. If you keep proper backups what you can do is when you pick up those extra hard drives and have enough to move over to the new system you could rebuild your pool with all of your disks and restore from backup. For example, start with a two-disk mirror vdev as the only vdev in the pool; add 1 more two-disk mirror vdev when you can afford it; finally once you pick up the last two disks rebuild the pool as a six-disk RAIDZ2 vdev.

 

[Chris Moore]

Why would it not work at all? I’ve seen it suggested here when someone wanted to transition from a 2-drive mirror to a 3-drive raidz1. My only concern is using the pool for weeks with a few drives offline.
The raid would start empty so there’s no legacy data to copy over.

You can't have that many drives missing. You could create the pool using files to back the redundancy, but ZFS RAIDz2 will fail with more than two drives missing.

 

[Chris Moore]

I am planning to have an 8 x 6TB pool and I would like to start with 2 drives (which I can have now) and create an 8-drive pool with 6 offline drives

Firstly, this is not possible at all from the GUI. You can create a file backed pool, from the command line, but your pool capacity is limited by the capacity of the smallest disk. You wouldn't be able to put any data into the pool until you had a minimum of six drives that actually had available space.
Please read the refference material.

 

[Andreaux]

Firstly, this is not possible at all from the GUI. You can create a file backed pool, from the command line, but your pool capacity is limited by the capacity of the smallest disk. You wouldn't be able to put any data into the pool until you had a minimum of six drives that actually had available space.
Please read the refference material.

I will, Thank you for the links!!

At first, it seemed like a not-so-bad idea :)

I might go for the multiple 2-mirrors route then. I picture it like this. Please correct me if I’m wrong:

1. Create a 2-disk mirror
2. adding disks to further mirrors until I have all of them
3. backup all the data on the NAS so far to the last two (they’ll probably be enough at that point)
4. create a 8-disk pool with 2 disks offline,
5. copy the data to the pool
6. wipe the last 2 disks and add them to the pool, replacing the 2 offline ones

Does this sound feasible?

Thank you all for the comments so far!

 

[Chris Moore]

It could be done, but it is risky. No refunds.