Migrating boot devices

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Hybrice

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Hi guys,

A quick background, we deployed a server some time back with 12x 4TB disks, at the time we didn't have USB's spare and we were pressed for time so we installed the OS on 2x4TB (wasteful, I know), now we need the capacity and need to migrate to a pair of USBs.

My question, and please correct if wrong in any assumptions.

We simply;
1. Export the config file from the existing setup
2. Install FreeNAS on both the new USBs and boot from those
3. Import the config file
4. Flatten the disks and add them to the existing volume

Is that correct? All volumes will be retained, no data loss?
 

sretalla

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Your plan sounds good.

New install with old config backup uploaded will see the pools correctly and remember all other config like shares and VMs.
 

sretalla

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Assuming your setup is 2x4TB mirrored VDEVs, otherwise you may need to re-think what "adding to the existing volume" means.
 

Chris Moore

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sretalla

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So there will be a problem with your planned step number 4.

You can't expand a RAIDZ2 pool by adding disks. Backup, rebuild with the new disks in the pool, restore.
 

sretalla

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Well, if we were talking about RAID6 arrays, we'd be in another operating system, so I'm sure at least some of the time the answer would be that you can, but RAIDZ2 isn't RAID6 and currently can't be expanded (long term plans to release this functionality, but we're a few years out from it arriving in FreeNAS by all accounts).
 
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sretalla

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You can expand a pool by adding VDEVs, but this probably isn't what you were looking for as it has 3 key problems:

1. you should probably add a similarly configured VDEV (meaning another 10 disks in your case)
2. adding a second VDEV to a populated pool will not give you the right balancing to deliver the performance increase you might expect (at least not at first) ... think of a RAID 0 of 2 RAID arrays, but due to the late addition of the second RAID, all the writes will go to the new one until it's evened out.
3. Lose one VDEV (one of the RAIDZ2 sets loses 3 drives) and your whole pool (including the other RAIDZ2 VDEV) is dead... unlikely, but a new risk compared to a single VDEV RAIDZ2 pool.
 

Hybrice

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Is there any plug/addon or any CLI workaround to extend a vdev? (Does "zpool add" not work??) We weren't aware of this rather glaring issue at the start, it's unusual to see a storage platform unable to expand vdevs, given FreeBSD supports it natively?
 

MrToddsFriends

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Chris Moore

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Is there any plug/addon or any CLI workaround to extend a vdev? (Does "zpool add" not work??) We weren't aware of this rather glaring issue at the start, it's unusual to see a storage platform unable to expand vdevs, given FreeBSD supports it natively?
What makes you think that BSD supports it ?
 
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