difference between qemu cache settings and ceph.conf rbd cache settings?

difference between qemu cache settings and ceph.conf rbd cache settings?

[Stefan Priebe - Profihost AG]

Hello list,

i've now patched my qemu to include the qemu cache settings for rbd.

Now i can change my drive caching mode. But there are also these 
settings for global section in ceph.conf.

         rbd_cache = true
         rbd_cache_size = 33554432
         rbd_cache_max_age = 2.0

How do they influence or replace each other?

thanks
Stefan

Re: difference between qemu cache settings and ceph.conf rbd cache settings?

[Josh Durgin]

On 06/18/2012 11:37 PM, Stefan Priebe - Profihost AG wrote:
> Hello list,
>
> i've now patched my qemu to include the qemu cache settings for rbd.
>
> Now i can change my drive caching mode. But there are also these
> settings for global section in ceph.conf.
>
> rbd_cache = true
> rbd_cache_size = 33554432
> rbd_cache_max_age = 2.0
>
> How do they influence or replace each other?
>
> thanks
> Stefan

In qemu, the cache settings map to:

writeback:
   rbd_cache = true

writethrough:
   rbd_cache = true
   rbd_cache_max_dirty = 0

none:
   rbd_cache = false

qemu's settings are overridden by any custom settings you have in a
config file or on the qemu command line.

Josh

Re: difference between qemu cache settings and ceph.conf rbd cache settings?

[Stefan Priebe - Profihost AG]

Am 19.06.2012 08:42, schrieb Josh Durgin:
> In qemu, the cache settings map to:
>
> writeback:
> rbd_cache = true
>
> writethrough:
> rbd_cache = true
> rbd_cache_max_dirty = 0
>
> none:
> rbd_cache = false
>
> qemu's settings are overridden by any custom settings you have in a
> config file or on the qemu command line.

Thanks!

Stefan