On 11/04/2012 03:42 AM, Sage Weil wrote:
The wip-explicit-pgnum changes the 'ceph osd pool create <name> <pgnum>' command to require the pg_num value instead of defaulting to 8. This would make it harder for users to get this wrong.
I like this. It'd be great if we could add a pgnum argument to 'rados mkpool' and the corresponding librados pool_create* functions too.
On the other hand, it probably also breaks some scripts for deploying OpenStack that create volume and image pools. :/
If those scripts are creating pools with 8 pgs, they're going to create problems anyway. I don't mind breaking them as long as it's well documented (i.e. release notes and docs on 'ceph osd pool create' should mention the change).
Ideas? The original idea was that the monitor would automagically notice when a small pgnum pool gets lots of objects and trigger a split. Even if we don't do that, pretty soon now you'll be able to explicitly increase pg_num. I still think it might be a good idea to require it up-front, though.
Until split is implemented and well-tested, I think it makes sense to require it up-front. It's easy to relax that requirement later if we want to make it more automatic.
An alternative would be to default to a larger number (say, num_osds << 2). My concern there is that it makes it easy to create lots of pgs for pools that may be small, and it's still not large enough to get good performance for the "create pool, run rados bench" crowd.
It would also be easy to create too few pgs, and then add a bunch of osds later. Josh -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
