I added a third SSD to my cache and set the balance to -dconvert=raid5 -mconvert=raid1. It ran the balance and finished just fine. It's showing 1.5TB free instead of the 1TB I would expect from RAID5. Is this just a display error or is it actually going to try and fail to use that space?

Edited January 14, 20197 yr by mrgstiffler

It's a btrfs limitation with raid5/6, used spaced will show correctly, available space will not account for parity, but since it still decreases with used space not much of a problem, also note that while you can use raid5/6, I use it myself, it's still less stable than other profiles, and a UPS is strongly recommended because of the the write hole issue that affects most raid5/6 implementations.

 

 

 

 

 

 

 

 

That makes sense. Thanks.

So basically a 3 or 4 disc RAID5 cache tells you some wrong numbers but it works 100% correctly?

I am about to install 4 x 240gb ssd's as cache - or atleast that was the thought

I have 1 x 512GB PCIe NVME as cache right now and 1 x 256GB M.2 unassigned that im not sure how to use best way

Free space is incorrectly reported, also note that btrfs raid5/6 still has some issues.

10 hours ago, johnnie.black said:

Free space is incorrectly reported, also note that btrfs raid5/6 still has some issues.

So what setting to be bulletproof?

9 minutes ago, MWDK said:

So what setting to be bulletproof?

Nothing is bulletproof, btrfs raid1/0/10 is more stable then raid5/6, but I've been using several raid5 pools for some time now without issues, just make sure any important data is regularly backed up, as it should always be.