Re: Best Practice: Add new device to RAID1 pool

[Cloud Admin <admin@cloud.haefemeier.eu>]

Am Montag, den 24.07.2017, 09:46 -0400 schrieb Austin S. Hemmelgarn:
> On 2017-07-24 07:27, Cloud Admin wrote:
> > Hi,
> > I have a multi-device pool (three discs) as RAID1. Now I want to
> > add a
> > new disc to increase the pool. I followed the description on https:
> > //bt
> > rfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices and
> > used 'btrfs add <device> <btrfs path>'. After that I called a
> > balance
> > for rebalancing the RAID1 using 'btrfs balance start <btrfs path>'.
> > Is that anything or should I need to call a resize (for example) or
> > anything else? Or do I need to specify filter/profile parameters
> > for
> > balancing?
> > I am a little bit confused because the balance command is running
> > since
> > 12 hours and only 3GB of data are touched. This would mean the
> > whole
> > balance process (new disc has 8TB) would run a long, long time...
> > and
> > is using one cpu by 100%.
> 
> Based on what you're saying, it sounds like you've either run into a 
> bug, or have a huge number of snapshots on this filesystem.  

It depends what you define as huge. The call of 'btrfs sub list <btrfs
path>' returns a list of 255 subvolume.
I think this is not too huge. The most of this subvolumes was created
using docker itself. I cancel the balance (this will take awhile) and will try to delete such of these subvolumes/snapshots.
What can I do more?

> What you 
> described is exactly what you should be doing when expanding an
> array 
> (add the device, then run a full balance).  The fact that it's
> taking 
> this long isn't normal, unless you have very slow storage devices.