6.9.1 - Cache Drives not using all drive space (5 devices)

[Joel Rieger]

I have a cache pool configured on an upgraded 6.9.1 server.  I have already removed and rebuilt the cache pool to align at the 1MB per the 6.9.1 instructions.  The pool consists of the following (all SSD devices):

1TB SSD

500GB SSD

256GB SSD

120GB SSD

120GB SSD

 

These are configured in the standard RAID1 btrfs-encrypted format.  The issue is that I am getting is that the cache array only reports ~618GB free, where it use to report almost 1TB free (~950+ish), which is what I would expect at a RAID1 btrfs arrangement.

 

Did something change in 6.9.x that might cause btrfs in the cache to not properly map to all of the drives?

 

From that space free, it looks like it is mapping 120GB to 120GB + 1TB to 500GB to equal 620GB.  In reality, it should be 1TB + all of the other drives as the second copy (as needed).  This use to work correctly so something changed, but I cannot get it to properly map the second copy of the data anymore.

 

Is there some way for me to force this or tell btrfs how to properly use the drives?

[JonathanM]

Are you sure the RAID volume is using all the drives? Posting diagnostics would show some info.

 

[Joel Rieger]

As far as I can tell, it is.  I looked through the logs and did not find any failures that appear linked, though it is possible I missed it.  I have posted a screenshot of my drives below as well as attached a diag download.

 

Thank you!

ej-unraid-01-diagnostics-20210316-2037.zip

[ChatNoir]

I think that there is an issue with the reported free space for BTRFS if you have an odd number of devices. The total space should be OK though.

It is a BTRFS issue.

 

JorgeB could confirm this as he knows more about this stuff.

[JorgeB]

2 hours ago, ChatNoir said:

I think that there is an issue with the reported free space for BTRFS if you have an odd number of devices. The total space should be OK though.

It is a BTRFS issue.

Correct, free space will be incorrect, though it will get better as you fill up the pool.

[Joel Rieger]

So there is a TB of space that can be used by unraid, and as I use more of the cache array, it will slowly correct itself?  Interesting.  Ok, thank you!  I appreciate the information!

 

[JorgeB]

39 minutes ago, Joel Rieger said:

So there is a TB of space that can be used by unraid, and as I use more of the cache array, it will slowly correct itself? 

Correct, the more space you use the more accurate the reported free space will be.