On Thu, Oct 18, 2012 at 03:28:17PM +0200, Spelic wrote: > So, supposing one is aware of this problem beforehand, at pool creation > can this problem be worked around by using --poolmetadatasize to > make a metadata volume much larger than the default? > > And if yes, do you have any advice on the metadata size we should use? There are various factors that effect this. - block size - data dev size - nr snapshots The rule of thumb I've been giving is: work out the number of blocks in your data device. ie. data_dev_size / data_block_size. Then multiply by 64. This gives the metadata size in bytes. The above calculation should be fine for people who're primarily using thinp for thin provisioning, and not lots of snapshots. I recommend these people use a large block size. eg, 4M. I don't think this is what lvm does by default (at one point it was using a block size of 64k). Snapshots require extra copies of the metadata for devices. Often the data is shared, but the btrees for the metadata diverge as cow exceptions occur. So if you're using snapshots allocate more space. This is compounded by the fact that it's often better to use small block sizes for snapshots. - Joe _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
