Hello, I am experimenting with adding a SSD-Cache tier to my existing Ceph 0.94.5 Cluster. Currently I have: 10 OSDs on 5 hosts (spinning disks). 2 OSDs on 1 host (SSDs) I have followed the cache tier docs: http://docs.ceph.com/docs/master/rados/operations/cache-tiering/ 1st I created a new (spinning pool) and set up the SSDs as a cache tier. All is fine. I can create/access images with rbd. I can seed that it is used with "rados -p cache-pool ls" Now, when I add a cache pool to my existing pools, for example the one which hosts all my VM images all hell breaks loose. The VMs all get I/O end request errors and remount their filesystems R/O. If I shut them down and try to start them again, they won't start, virsh gives me an error "cannot read metadata header" (or something like that). Also, "rados -p cache-pool ls" hangs forewer. I have read here: https://software.intel.com/en-us/blogs/2015/03/03/ceph-cache-tiering-introduction that adding caches works on-the-fly. Is there a special trick to add cache to a running, pool under load (which is not very high, though)? And what about the "osd tier add-cache <poolname> <poolname> <int>" command? its supposed to add a cache to the 1st pool. I can't see this be used in bost of the above links. Thanks very much, udo.
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