On Oct 13, 2014, at 7:20 AM, Kees de Jong <keesdejong@gmail.com> wrote: > Hi, > > > > The documentation is not clear about how big the cache size should be > for optimal performance. It only gives pointers about how big the meta > data for the cache should be. > > "Create the cache metadata LV. This LV will hold cache pool metadata. > The size of this LV should be 1000 times smaller than the cache data > LV, with a minimum size of 8MiB." > > There is however an example in the man page with a 100GB OriginLV > which apparently needs (at least) 10GB of cache size. But what is the > math? I for example have 4 LV's I want to cache. 6GB, 60GB, 100GB and > 2TB and I have a 240GB SSD which will act as the caching disk. > > Could someone please fill in the gaps here? It really does depend on your workload. We don’t have any general advice yet that I can share on how large the overall cache should be relative to the LV it is caching. (We can compute how much space is needed for the metadata area for a given cache, which is why we can give advice on those numbers.) You could try out various sizes and see what happens. You could also do it a bit more deterministically by watching the number of used cache blocks vs the total cache blocks for you workload, as well as checking other reported metrics such as read/write hits/misses. Currently, this information is had from ‘dmsetup status’. brassow _______________________________________________ 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/
