On Sun, Jan 15, 2017 at 2:56 PM, Shawn Edwards <[email protected]> wrote: > If I, say, have 10 rbd attached to the same box using librbd, all 10 of the > rbd are clones of the same snapshot, and I have caching turned on, will each > rbd be caching blocks from the parent snapshot individually, or will the 10 > rbd processes be building up their own cache, ignorant of the other > process's caching?
Each process will utilize its own, independent cache for the parent image. There is no interprocess coordination to share the cache bits. > The use case I have is a lot of rbd-nbd mounted rbd used as VM boot disks > all based on the same clone. It would be great if the parent clone could be > cached once and then only blocks which were copy-on-write were in each > individual process's cache. If you are worried about the footprint, you could disable the use of the cache within just the parent image by running "rbd metadata set <image spec> conf_rbd_cache false" against the parent image. Since you are using a VM on top of librbd, the librbd cache is effectively a L2 cache so you probably aren't gaining much by caching reads for the parent image since the VM will most likely cache the reads as well. -- Jason _______________________________________________ ceph-users mailing list [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
