Re: btrfs raid1 balance slow

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On Mon, Jan 20, 2020 at 11:08:40PM +0100, kjansen387 wrote:
> I had a btrfs raid1 with 2 4TB SATA 5400RPM disks . Regular disk I/O is
> about 2MB/sec per drive, ~40IOPS, mostly write. I had ~150GB free and added
> one 2 TB disk and started the balance:
> 
> btrfs device add -f /dev/sdb /export
> btrfs filesystem balance /export
> 
> It's now running for 24 hours, 70% remaining:
> 
> # btrfs balance status -v /export
> Balance on '/export' is running
> 1057 out of about 3561 chunks balanced (1058 considered),  70% left
> Dumping filters: flags 0x7, state 0x1, force is off
>   DATA (flags 0x0): balancing
>   METADATA (flags 0x0): balancing
>   SYSTEM (flags 0x0): balancing
> 
> I have searched for similar cases, but, I do not have quotas enabled, I do
> not have compression enabled, and my CPU supports sse4_2 . CPU (i7-8700K) is
> doing fine, 80% idle (average over all threads).

   Do you have lots of snapshots? It can take a lot of time on some of
the metadata chunks if there's lots of shared extents.

> Is this normal ? I have to repeat this process 2 times (adding more 2TB
> disks), any way I can make it faster ?

   Cancel the current balance, add the remaining disks, and then
balance only once you've added them all.

   Hugo.

-- 
Hugo Mills             | If it's December 1941 in Casablanca, what time is it
hugo@... carfax.org.uk | in New York?
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                               Rick Blaine, Casablanca



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