Re: Finding out via librados if a cluster is near full

[Wido den Hollander <wido@42on.com>]

On 05/29/2013 10:14 AM, Wido den Hollander wrote:
> Hi,
>
> Is there a way to find out if a cluster is near full via librados?
>

Yes, there is. (Thanks tnt on IRC!)

There is ofcourse rados_cluster_stat which will give you:

struct rados_cluster_stat_t {
   uint64_t kb, kb_used, kb_avail;
   uint64_t num_objects;
};


One thing here is however that you don't know to what the (near)full 
ratio has been set to. So you have to do your own guessing.

> The reason I'm asking is that I'm working on a deployment of the RADOS
> Gateway and one of the potential problems I see is that the RADOS
> Gateway can keep writing and filling up the whole cluster.
>

So, with the cluster stat information we could implement:

rgw_refuse_write_above_ratio DOUBLE 0.90

> It's obvious that it's the admin's responsibility to make sure that
> doesn't happen, but what I'd like to do is make the RADOS Gateway deny
> PUT requests when the cluster is near full.
>
> That way normal meta data operations (thus writes) can continue, but new
> objects won't be accepted until the cluster has enough space available.
>
> This might also be useful for librbd. Refuse the creation of new RBD
> images so that existing images can continue operating.
>


-- 
Wido den Hollander
42on B.V.

Phone: +31 (0)20 700 9902
Skype: contact42on