On Thu, Jul 21, 2011 at 9:25 AM, Colin Patrick McCabe <colin.mccabe@xxxxxxxxxxxxx> wrote: > On the other hand, there is some fixed overhead to having multiple > cosd processes running. RAIDing a few disks might be a good option if > the fixed overhead of having a cosd per disk is too much. This in particular is important. In general the cosd processes won't use much CPU or memory, but in some situations (like recovery) they can spike in a correlated fashion that ends up causing OSD flapping. These behavior characteristics aren't well-modeled yet simply because there's bug fixing still going on in those code paths (and some optimization), but it's something to be aware of. I think you want something like 1GHz of a modern core per cosd to handle this, even though a stable system will often do just fine running 4 cosds on an Atom. (Presumably we can bring these requirements down once we move on from stabilization to performance.) -Greg -- 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
