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bkastner

Cache Pool Question

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So... I currently have a 1TB WD Black cache drive which I am looking at replacing with a NVMe 1TB drive, and I was thinking of getting a second one as well and adding it to a cache pool.

 

I've seen the documented process for swapping the cache drive, but was curious whether you could instead just add the 1TB NVMe to a cache pool with the WD, and then remove the WD drive from the pool, leaving the NVMe with everything going. 

 

If I read cache pools correctly both drives maintain a copy of the data, so is this a doable solution? Also... if I start with the one NVMe cache drive, can I add a second one for redundancy down the road? Or should I be adding them both at the same time?

 

My current cache drive is basically empty as I've been preparing for this move, but was curious if the above replace/migrate was a valid approach or if there was a reason that woudln't work (other than speeds would be quite different between a HDD and NVMe drive of course).

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9 hours ago, bkastner said:

I've seen the documented process for swapping the cache drive, but was curious whether you could instead just add the 1TB NVMe to a cache pool with the WD, and then remove the WD drive from the pool, leaving the NVMe with everything going.

You can if current one it's btrfs, but it would me much quicker to do and online replacement instead, you can replace a btrfs single device "pool", see here.

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Thanks for the info. I've reformatted my new drive as BTRFS and finished the standard migration to it. 

 

Am I correct that if I add a second BTRFS NVMe drive to the system I can add it to the cache as well and they will automatically sync data between the two providing redundancy?

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37 minutes ago, bkastner said:

Am I correct that if I add a second BTRFS NVMe drive to the system I can add it to the cache as well and they will automatically sync data between the two providing redundancy?

Yes, by default it creates a raid1 pool.

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Okay... one more question... I am 99.99999% positive I reformatted the new cache drive as btrfs, but just noticed it's showing as xfs in Unraid.... I am almost done moving the 250GB of Plex data back over (1.5M files) which take such a long time. Am I screwed now for adding a second cache drive and getting the raid1 pool? Does it need to be btrfs to support that? Or does xfs work? 

 

I really hope the answer is that I am good, but I am guessing I am likely not.

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Only btrfs supports pools, xfs can only be single device.

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