On 2012-05-29, at 1:28 PM, Peter Grandi wrote: >> The tar backup of the MDT is taking a very long time. So far it has >> backed up 1.6GB of the 5.0GB used in nine hours. In watching the tar >> process pointers to small or average size files are backed up quickly >> and at a consistent pace. When tar encounters a pointer/inode >> belonging to a very large file (100GB+) the tar process stalls on that >> file for a very long time, as if it were trying to archive the real >> filesize amount of data rather than the pointer/inode. > > If you have stripes on, a 100GiB file will have 100,000 1MiB > stripes, and each requires a chunk of metadata. The descriptor > for that file will have this potentially a very large number of > extents, scattered around the MDT block device, depending on how > slowly the file grew etc.
While that may be true for other distributed filesystems, that is not true for Lustre at all. The size of a Lustre object is not fixed to a "chunk size" like 32MB or similar, but rather is variable depending on the size of the file itself. The number of "stripes" (== objects) on a file is currently fixed at file creation time, and the MDS only needs to store the location of each stripe (at most one per OST). The actual blocks/extents of the objects are managed inside the OST itself and are never seen by the client or the MDS. Cheers, Andreas -- Andreas Dilger Whamcloud, Inc. Principal Lustre Engineer http://www.whamcloud.com/ _______________________________________________ Lustre-discuss mailing list [email protected] http://lists.lustre.org/mailman/listinfo/lustre-discuss
