On 2020/12/10 上午9:52, Eric Wheeler wrote:
> Hello all,
> 
> We have a 30TB volume with lots of snapshots that is low on space and we 
> are trying to rebalance.  Even if we don't rebalance, the space cleaner 
> still fills up the Global reserve:
> 
>     Device size:                  30.00TiB
>     Device allocated:             30.00TiB
>     Device unallocated:            1.00GiB

So it still has one GiB unallocated for rebalance.

But, don't expect much luck, as balance is not the solution to your problem.
What you really need is to free up some metadata space, as you're really
exhausting the metadata space (only 1GiB available for new metadata)

>     Device missing:                  0.00B
>     Used:                         29.27TiB
>     Free (estimated):            705.21GiB	(min: 704.71GiB)
>     Data ratio:                       1.00
>     Metadata ratio:                   2.00
>>>> Global reserve:              512.00MiB	(used: 512.00MiB) <<<<<<<
> 
> This was on a Linux 5.6 kernel.  I'm trying a Linux 5.9.13 kernel with a 
> hacked in SZ_4G in place of the SZ_512MB and will report back when I learn 
> more.

It won't change. In fact, if you increase the global rsv to 4G, it would
cause more problem since btrfs will try to reserve more metadata space,
which you definitely don't have.
> 
> In the meantime, do you have any suggestions to work through the issue?

If you can still remove files/snapshots, do it.

Thanks,
Qu
> 
> Thank you for your help!
> 
> 
> --
> Eric Wheeler
>