tcharron

I think that was related to an an unbalanced pool (which needed a btrfs balance to correct).
 
I removed my 240GB drive from the pool.  Unraid now reports usuable space on the pool of 511GB (formerly 512GB).  Note that the pool size went down (from 589GB to 477GB), but used and available did not change whatsoever, despite removal of the 240GB drive ! :
 
# btrfs fi usage -T /mnt/cache Overall: Device size: 953.88GiB Device allocated: 426.06GiB Device unallocated: 527.82GiB Device missing: 0.00B Device slack: 0.00B Used: 422.18GiB Free (estimated): 264.25GiB (min: 264.25GiB) Free (statfs, df): 264.25GiB Data ratio: 2.00 Metadata ratio: 2.00 Global reserve: 264.42MiB (used: 0.00B) Multiple profiles: no Data Metadata System Id Path RAID1 RAID1 RAID1 Unallocated Total Slack -- --------- --------- --------- -------- ----------- --------- ----- 1 /dev/sdf1 211.00GiB 2.00GiB 32.00MiB 263.91GiB 476.94GiB - 2 /dev/sdj1 211.00GiB 2.00GiB 32.00MiB 263.91GiB 476.94GiB - -- --------- --------- --------- -------- ----------- --------- ----- Total 211.00GiB 2.00GiB 32.00MiB 527.82GiB 953.88GiB 0.00B Used 210.66GiB 444.53MiB 48.00KiB # df /mnt/cache Filesystem 1K-blocks Used Available Use% Mounted on /dev/sdf1 500107080 221614288 277087344 45% /mnt/cache # df /mnt/cache -h Filesystem Size Used Avail Use% Mounted on /dev/sdf1 477G 212G 265G 45% /mnt/cache  
This is a big win from my perspective -- one less drive in the system with no downside.  
 
Also worth mentioning for anyone who finds this... the carfax calculator I linked to above is wrong (since it showed 0 unusable space) !