Trim SSD's on 6.9


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1 minute ago, JorgeB said:

It's not necessary for btrfs pools, still is if you use XFS.

 

That is the fastest response I have ever gotten. Has the recommendation changed on what filesystem to use for cache/pool drives? I was always told btrfs only for multiple drives, otherwise XFS due to stability.

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3 minutes ago, JorgeB said:

XFS is the best choice for most users using single device cache, unless you need the btrfs features.

 

Thank you sir. It occurs to me that I had read before that the primary hang up with using SSD's in the array was something to do with the way it handled trim. Is this possibly foreshadowing for this feature being made more possible in the near future?

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  • 3 weeks later...

Not only is the TRIM utility not useful for btrfs formatted SSDs (because TRIM is built in to btrfs) but it appears to be positively dangerous. My recently destroyed btrfs SSD cache drive was using the UnRAID TRIM utility (on advice from other UnRAID users)  and succumbed after a couple of months, turning read-only with the error:

 

cache and super generation don't match, space cache will be invalidated

 

If I'm reading this aright (always a big IF) and the current UnRAID implementation of TRIM is destructive on btrfs-formatted SSDs, shouldn't the utility be updated to detect btrfs, warn the user, and render itself inactive?

 

The good news is that only the btrfs formatting was destroyed. Reformatted as xfs, the SSD lives on. But if I can get confirmation of my assertions here, I'm inclined to return the SSD to btrfs.

 

-- 

Chris

Edited by bidmead
spelling correction
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1 minute ago, bidmead said:

Not only is the TRIM utility not useful for btrfs formatted SSDs (because TRIM is built in to btrfs) but it appears to be positively dangerous.

It's perfectly fine to run trim on btrfs filesystems.

 

1 minute ago, bidmead said:

cache and super generation don't match, space cache will be invalidated

This is just a warning, unrelated to trim, and not a reason to make a filesystem read-only, something else must have happened.

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Good question, @John_M. It's all set out in the UnRAID story. The SSD in question uses RAISE and I did ask the forum earlier whether this made an external TRIM utility redundant but the response seemed to be to go ahead with TRIM anyway.

 

I still have my doubts about whether the combination of btrfs, TRIM and RAISE may not be asking for trouble. I understand that OWC, the manufacturer, is currently investigating this. Meanwhile, I'm running the SSD, now happily formatted as xfs. TRIMmed weekly, uneventfully.

 

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Chris

Edited by bidmead
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  • 2 months later...
  • 4 months later...

Redundancy was the plan... I'm refreshing my server, so maybe I'll see how it handles without cache. Is this topic documented anywhere? Is it as simple as adding a second btrfs SSD, moving files over, then switching the current SSD to btrfs and adding it back?

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