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Difference between 'replace' disk and remove from pool then add new

Western Digital Drives - The Preferred Drives of FreeNAS and TrueNAS CORE
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Intel

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Sep 30, 2014
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Hi guys

I am in the process of upgrading my ZFS raidz 3x 4TB array into 5TB disks... I have plugged in the new disk and 'replaced' via the web gui

This seems to work, but what is the difference of using 'replace' (it idles the old drive and starts resilvering the new disk) and plainly removing one old disk from array, then plugging in the new disk in its place?

is the 'replace' method safer since all data is left on the old disk, while the new disk is being resilvered?
 

m0nkey_

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Oct 27, 2015
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This is covered in the documentation: http://doc.freenas.org/9.3/freenas_storage.html#replacing-drives-to-grow-a-zfs-pool

The safest way to perform this is to use a spare drive port or an eSATA port and a hard drive dock. In this case, you can perform the following steps:

  1. Shut down the system.
  2. Install one new disk.
  3. Start up the system.
  4. Go to Storage ‣ Volumes, select the pool to expand and click the “Volume Status” button. Select a disk and click the “Replace” button. Choose the new disk as the replacement.
  5. You can view the status of the resilver process by running zpool status. When the new disk has resilvered, the old one will be automatically offlined. You can then shut down the system and physically remove the replaced disk. One advantage of this approach is that there is no loss of redundancy during the resilver.
 

danb35

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is the 'replace' method safer since all data is left on the old disk, while the new disk is being resilvered?
Either way you're replacing a disk. If you have to offline a disk to make room for its replacement, though, your pool is degraded while the new disk is resilvering. If you can add the new disk, at least temporarily, without disconnecting the old one, the old one remains online until the new disk finishes resilvering, so you never lose any redundancy.
 

Intel

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Sep 30, 2014
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Thanks! since I have an extra SATA port by unplugging the DVD drive I will just do replace :)
 
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