If you are using RBD, and want to avoid potential image corruption, add filestore fiemap = false to the [osd] section of your ceph.conf and restart your OSDs. We've tracked down the source of some corruption to racy/buggy FIEMAP ioctl behavior. The RBD client (when caching is diabled--the default) uses a 'sparse read' operation that the OSD implements by doing an fsync on the object file, mapping which extents are allocated, and sending only that data over the wire. We have observed incorrect/changing FIEMAP on both btrfs: fsync fiemap returns mapping <time passes, no modifications to file> fiemap returns different mapping Josh is still tracking down which kernels and file system are affected; fortunately it is relatively easy to reproduce with the test_librbd_fsx tool. In the meantime, the (mis)feature can be safely disabled. It will default to off in 0.48. It is unclear whether it's really much of a performance win anyway. Thanks! sage -- 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
