Hi all,

 

I have been having issues with my system hanging which has been a result of a full cache drive. However, I have two cache drives in the pool (a 64GB and a 240GB) and the GUI is showing that I have 90GB free still.

 

What is going on here?

masterstructure-syslog-20160212-1553.zip

Free space is incorrectly reported when using different size disks, btrfs limitation,  your max usable space is 64GB.

Ok thanks!

 

So the max size of the cache pool is the size of the smallest drive? what is the point of having a cache pool then?

Ok thanks!

 

So the max size of the cache pool is the size of the smallest drive? what is the point of having a cache pool then?

Redundancy. It can be changed to Raid0, so you can use all the space.

I feel embarrassed that I didn't know this. Is there a a wiki site or manual for the cache pool? How would I convert to RAID0. It sounds like I would need to backup my filesystem and reconfig it to RAID0.

I found this in another thread that should convert it to Raid1.

 

-dconvert=raid0 -mconvert=raid1

 

 

Is there a information resource for the cache pool? I couldn't find one.

That's the correct way to convert, there's not much cache pool documentation.

Ok thanks!

 

So the max size of the cache pool is the size of the smallest drive? what is the point of having a cache pool then?

This is true if you have two drives in the cache pool.  With more than two drives then the available size is more complicated as it is whatever can lead to having the data on two drives.  e.g. 64GB + 128GB + 240GB would give you 192GB of usable space.  There is a calculator (I do not have the URL to hand) where you can enter the sizes for the disk in a BTRFS pool and be told the amount of usable space.

btrfs disk usage calculator