Re: Balance on 5-disk RAID1 put all data on 2 disks, leaving the rest empty

[Anand Jain <anand.jain@oracle.com>]

On 10/26/23 05:15, Roman Mamedov wrote:
> On Wed, 25 Oct 2023 17:08:08 -0400
> Remi Gauvin <remi@georgianit.com> wrote:
> 
>> On 2023-10-25 4:29 p.m., Peter Wedder wrote:
>>> Hello,
>>>
>>> I had a RAID1 array on top of 4x4TB drives. Recently I removed one 4TB drive and added two 16TB drives to it. After running a full, unfiltered balance on the array, I am left in a situation where all the 4TB drives are completely empty, and all the data and metadata is on the 16TB drives. Is this normal? I was expecting to have at least some data on the smaller drives.
>>>
>>
>> Yes, this is normal.  The BTRFS allocates space in drives with the the
>> most available free space.  The idea is to balance the 'unallocated'
>> space on each drive, so they can be filled evenly.  The 4TB drives will
>> be used when the 16TB dives have less than 4TB unallocated.
> 

Correct. That's the only allocation method we have at the moment. Do you
have any feedback on whether there are any other allocation methods that
make sense?

Thanks, Anand

> Interesting question and resolution. I'd be surprised by that as well.
> 
> Now, a great chance to "btrfs dev delete" all three remaining 4TB drives and
> unplug them for the time being, to save on noise, heat and power consumption!