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From Wido den Hollander <w...@widodh.nl>
Subject Custom properties for storage pools / volumes
Date Fri, 08 Feb 2013 13:42:48 GMT
Hi,

While thinking about the new features for RBD in 4.2 I've stumpled upon 
something.

RBD knows something like 'writeback caching' [0] and is enabled by 
adding rbd_cache=1 to the disk.

<disk>
  <source protocol='rbd' name='cloudstack/uuid'>
   <host name='monitor.ceph.XXX.nl' port='6789'/>
  </source>
</disk>

Now, if I want to enable RBD caching I'd do:

<disk>
  <source protocol='rbd' name='cloudstack/uuid:rbd_cache=1'>
   <host name='monitor.ceph.XXX.nl' port='6789'/>
  </source>
</disk>

One could say that I'd enable RBD caching, but there could be use cases 
where one would prefer data consistency over performance.

Now this is an example for RBD, but it also goes for QCOW2:

<disk type='file' device='disk'>
   <driver name='qemu' type='qcow2' cache='none'/>
</disk>

The cache[1] here can be set to writeback, writethrough or none. 
Depending on the use-case some people also might want to use write-back 
caching here.

Now, I'm just taking caching examples here, but it could also be that 
other SANs in the future want other custom properties, we never know.

I'm not so familiar with Xen and VMware, but maybe you also have some 
settings you want to control there?

I'd like to be able to set these settings per disk offering if possible, 
but otherwise it could be done per pool.

Going through the new storage subsystem I haven't been able to find 
anything that fits the needs here.

Ideas?

Wido

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