March 18, 201610 yr I currently have 2 SSD's assigned to my cache pool. One is a 120 GB and the other is a 240 GB. However when I look at the total size it says 180 GB, and when I go into the "Cache 2" device it doesn't even show as mounted. What am I missing here? Why does it show 180 GB instead of 360 GB? Why does "Cache 2" just have a "-" in the "File system status:" section?
March 18, 201610 yr Community Expert Btrfs limitation, space is incorrectly reported when using raid1 whit different size disks. BTW, your actual usable space is 120GB, anymore and you’ll get disk full error.
March 18, 201610 yr Author Oh. Is the cache pool automatically a RAID 1? I read about people making their cache pool into a RAID, but I didn't see anything that said it was automatic. I kind of thought it was treated like the others and simply added on top of each other.
March 18, 201610 yr Community Expert It's raid1 by default, you can change to raid0 if you want more space without redundancy.
March 18, 201610 yr Author Huh, I see. So by default it is not the best idea to have different sized SSD's in the cache pool since it will only be the size of the smallest drive? How does one change from RAID 1 to RAID 0? I can't seem to find any instructions on how to accomplish this. I'm thinking that I might want to change this in the future.
March 18, 201610 yr Bring up your cache settings and change the balance to: -dconvert=raid0 -mconvert=raid1 Myk
March 19, 201610 yr Author Btrfs limitation, space is incorrectly reported when using raid1 whit different size disks. BTW, your actual usable space is 120GB, anymore and you’ll get disk full error. Bring up your cache settings and change the balance to: -dconvert=raid0 -mconvert=raid1 Myk Thanks for the information! That was exactly what I was wanting to know.
March 19, 201610 yr In raid 0 you are still limited by your smallest disk so you will will only have 240 GB.
March 19, 201610 yr In raid 0 you are still limited by your smallest disk so you will will only have 240 GB. How do you figure?
March 19, 201610 yr Community Expert In raid 0 you are still limited by your smallest disk so you will will only have 240 GB. True, with different size disks to use all capacity you have to convert to single profile: -dconvert=single -mconvert=raid1 This is the BTFRS equivalent of JBOD. Metadata can still stay raid1, as it takes up very little space, and redundancy can be good.
March 20, 201610 yr Btrfs limitation, space is incorrectly reported when using raid1 whit different size disks. BTW, your actual usable space is 120GB, anymore and you’ll get disk full error. Bring up your cache settings and change the balance to: -dconvert=raid0 -mconvert=raid1 Myk Thanks for the information! That was exactly what I was wanting to know. My statement is correct - all that is needed is above and it will put the two drives into a single 360g unprotected cache drive - no need to do the convert as listed above Myk
March 20, 201610 yr Community Expert My statement is correct - all that is needed is above and it will put the two drives into a single 360g unprotected cache drive - no need to do the convert as listed above Myk Afraid not, in this case using raid0 will give 240GB usable space (although free space it will be incorrectly reported as 360GB), only single profile will use the full 360GB.
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