[Openstack] swift ringbuilder and disk size/capacity relationship
Peter Brouwer
peter.brouwer at oracle.com
Wed Mar 9 11:03:30 UTC 2016
On 08/03/2016 02:26, Mark Kirkwood wrote:
> On 06/03/16 21:15, Peter Brouwer wrote:
>> Interesting info.
>> Two followup questions,
>> Can the ring builder cope with a disk that is dynamic in size, like
>> an nfs share from a storage array in which an nfs share shares
>> capacity from a pool, i.e. If an other share in that pool takes up
>> space the nfs share used by swift decrease in capacity.
>> So the thing Im trying to understand is how swift/ringbuilder checks
>> if a disk in a ring is running out of space?
>
> Well, you build the ring 'offline' and distribute the resulting files
> (object.ring.gz etc) to all the hosts in your Swift cluster. So the
> ring-builder binary does not have any idea about the free space
> available on a device (the builder - you - just plugs the weights in).
Indeed, I should have been a bit more clear with my question.
What is swifts behavior of a situation in which a disk where a swift
partition points to runs out of space? There can be a number of swift
partitions that point to the same disk, does each partition gets a
certain capacity of the disk allocated?
>
> Once Swift is up and running, you can check the state of things with
> swift-recon - which does know about free space, but I think a device
> that can *decrease* in capacity is not an ideal choice(!) - usual
> practice is to use a (real) disk dedicated to Swift storage.
>
> Additionally attaching devices via nfs is less than ideal too (adding
> additional network latency for one thing), and will make less useful
> some of Swift's locality optimisations (e.g affinity...since a host's
> nfs mounted 'device' might not actually be close to it)! Also nfs
> general vagueness regarding file locking and syncing make it seem like
> a bad choice overall.
Anyone have any experiences around locking issues. I've seen comments
elsewhere that locking contention might be an issue for disk space used
for container and account rings.
>
> regards
>
> Mark
--
Regards,
Peter Brouwer, Principal Software Engineer,
Oracle Application Integration Engineering.
Phone: +44 1506 672767, Mobile +44 7720 598 226
E-Mail: Peter.Brouwer at Oracle.com
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