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Reordering Data Drives in Snapraid config? (alien.top)

submitted 2 years ago by RileyKennels@alien.top to c/datahoarder@selfhosted.forum

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I've read that changing the name of data disks in Snapraid is tolerated. However to my understanding changing the order of data drives in the Snapraid config will cause issues with parity.

For example when replacing two smaller disks for one larger 18TB HDD, I run into the issue:

Data Disks:

d1-Exos10tb (this drive to be replaced with larger HDD)

d2-Exos-8tb (drive also to be replaced with same large HDD from above)

d3-Exos20tb

d4-Exos16tb

d5-Exos14tb

I wish to replace d1 and d2 with one large HDD. How would I go about this operation?

If I just assign the new larger data disk as d1, what would happen to d2 and the the drives listed after it? Should I comment out the d2 line until I utilize that position with another drive, preserving the following disk's order? Or is there a better way to go about this?

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[–] HTWingNut@alien.top 1 points 2 years ago (2 children)

Remove Disk 1 and then Disk 2 from the array using SnapRAID's suggestion:

https://www.snapraid.it/faq#remdatadisk

To remove a data disk from the array do:

Change in the configuration file the related "disk" option to point to an empty directory

Remove from the configuration file any "content" option pointing to such disk

Run a "sync" command with the "-E, --force-empty" option: snapraid sync -E

The "-E" option tells at SnapRAID to proceed even when detecting an empty disk. When the "sync" command terminates, remove the "disk" option from the configuration file. Your array is now without any reference to the removed disk.

Then add the new disk as d1 (it's ok to not have a 'd2' entry) with your consolidated data on it.

Then perform a new sync.

It will likely take as long as a fresh sync, so you may just want to start from scratch. At least I would. One time parity generation and you're back in business.

[–] EasternNotice9859@alien.top 1 points 2 years ago (1 children)

If you follow the steps above you will effectively discard all the existing checksums for the files on d1 and d2 and generate them anew. From an integrity pov it's not optimal.

Better to:

replace d1 with the new larger disk
move all files from d2 to the new larger disk (see 'How can I safely move files from one disk to another?' in the FAQ)

This is an outline, not step-by-step. If OP wants step-by-step for these then ask. But the manual & FAQ covers most things.

[–] RileyKennels@alien.top 1 points 2 years ago

To clarify if replace d1 with the new larger disk as d1 what will I do with the following drive order? Especially d2. Because by adding d1 as the new larger drive am I going to throw the following drives out of order causing a mandatory recalculation on my checksums. Or is d2 to be commented out or skipped entirely in my config. A step by step might help me more.

P.s. I have referenced the manual and FAQ and it doesn't go into specifics regarding drive order in the config.

Thanks