Simon Lundell wrote: > Regarding directory fragmentation; is there any way to determine how > fragmented a dir is? Traversal time seems to be pretty useless as the > OS seems to cache directory contents. > > //Simon > > I don't see much hope doing that without accessing directly the directory inodes / extents. I've been reading the JFS layout paper available on the web site to better understand issues that the policy on directory extents allocation might have on performance. So far I don't understand properly enough how the directory entries table is stored and handled upon file creation / deletion. I fully understand what each structure is used for, it's just the physical layout that gives me headaches. But once I get it, I might start coding a fragmentation analyzer that directly counts files and directories extents / inodes using the internal JFS structs. That could help find out if fragmentation is really an issue on some filesystems, like those of Peer-Joachim Koch and Dave Crane.
I've already coded a little tool that first creates a pool of 5000 files of random sizes, then sequentially deletes and recreates a random number of those files in an infinite loop. That would imitate Dave Crane's system behaviour concerning heavy use of file creation / deletion. However, the script is a little hard on I/O and cpu (what a surprise :P) so I'm gonna create a fast 8 disk raid 0 array on one of my NAS and run the application at night when nobody is working. I want to see how big the directory entries table can grow and how that impacts on performance. From what I read so far, JFS is very scalable but yet I've got to understand why a read-only rsync is 3-4 times slower with my NASes using JFS than it was using XFS (same data, same hardware). I want to check fragmentation first. Charles ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Jfs-discussion mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/jfs-discussion
