FRAGAVOID, System_Management, a tool to prevent disk defragmentation Fragmentn Avoid, DEFRAG, Avoid ~98% of dsk frag, 30%+ Disk Speedup w/src Released by Acorn and GCE for the freeware CD or other general consumption. The Fragmentation Avoider This utility actively prevents most disk fragmentation from occurring, so that disks run less fragmented, and usually considerably faster. It can be set up and left running with no attention; you configure it, turn it on, and forget it, enjoying faster I/O and disks that grow fragmented much more slowly than before. Your access to disks does not change at all in detail. This utility for Vax or Alpha came out of the Safety product available from General Cybernetic Engineering and was extended by Acorn Software to make its user interface more usable. It is presented in source as a "calling card"; we hope that you will look over the SPDs for the Acorn products and for the Safety components DPS and EACF in this area. They provide many services for storage management unavailable from any other places and include a complete "operator in a box" solution for tape jukeboxes, a cluster-aware disk jukebox solution that allows failover, and does not exhaust the MSCP server, full function, multi-level HSM, realtime compressing storage (disk space trebler), reliable user UNDELETE (which turns deletion to a "move to wastebasket"), and vast extensions to VMS file security. Now to the Frag Avoider. The frag avoider will largely prevent disks from becoming fragmented and will speed up disk access. In a nutshell, FA causes file extends to be a fraction of the initial file size (with some safeguards so the disk isn't filled etc.) so that VMS will not need to extend it as often. This results in files less fragmented than they otherwise would be, and writing doesn't need to "go to the well" as often. Some tests of random loads have shown up to a 30% speedup. (Enjoy!!) It also by this means, and by doing extends Contig Best Try, reduces the amount of "chaff" space in the extent cache, so your files tend to be placed with a "first fit" algorithm. The reduced fragmentation speeds read access. It will not interfere with normal operation or even disk defragmenters, but if you are nervous it can be turned off or on when you want. Normally it is expected to be set up in your systartup_vms script however. FA has been in use at several sites for a few years now. VMS disks in ordinary operation become fragmented rather quickly once defragmented. This leads to files which require many index file reads to locate and to lots of unnecessary disk head motion. On optical disks, this is an even worse problem, since seek times are much longer than magnetic disks. There are several reasons for this rapid refragmentation which deserve exploration. First is the way VMS uses its "extent cache". Whenever disk space is released, pointers to it are kept in memory awhile, so that space can be quickly allocated. The problem is that whenever files are closed, they are generally truncated to return extra allocated space to the system. The returned space is usually in small pieces, and thus new space requests wind up being satisfied from the last bunch of these little pieces of disk, rather than from larger areas. When files are deleted, they leave these pieces around which only get cut up still more with time. The result is fragmentation. Also, it is often the case that files are left open for fairly long times, and grow a few blocks at a time, typically allocating the volume default allocation, but sometimes allocating a small fixed number of blocks. Many of these files may grab 5-block extents thousands of times over their lives; this inevitably produces badly fragmented files which are hard to defragment because they're open. It also wastes a lot of time calling the file system for every few blocks. The Fragmentation Avoider is a system for automatically addressing these problems, and incidentally solving a few others. The Fragmentation Avoider arranges for file extension to be done "Contiguous Best Try" when this is possible. This causes VMS to flush (i.e., forget about) its extent cache and attempt to find a space big enough to hold the whole requested area before using badly fragmented store. The program can do this for every extension (the default and recommended behavior) or every Nth extension, if you feel the need to have the extent cache used, but cleared periodically. Fragmentation Avoider also controls the amount of space requested when a program extends a file (i.e., makes it longer). It can set a minimum extent request, so even explicit requests for one block at a time can be increased, and is able to request that a file be extended by 1/N of its current size, subject to free space constraints on the volume and a maximum extend amount. It will always request at least as much space as the program wanted, but will attempt to extend by 1/N of the file size, 1/8 of the available free space on the disk, or the maximum extent request, whichever is least. File extension is an expensive operation; by arranging it to be less often needed, F.A. can permit file writing to enjoy up to a 30% speed gain, in addition to permitting faster access to files written with it. This is the gain from not having to do the extend operation as often. SUMMARY: Fragmentation Avoider permits disk fragmentation to be controlled by altering somewhat the VMS file extend operation in a way that greatly slows the refragmentation of disk space. The package can be installed on any disks where this is desired and its parameters can be set on a per-disk basis. Disks where the Fragmentation Avoider is not installed are unaffected. Installation: See the AAAREADME.TXT. FA is installed with VMSINSTAL. (And don't forget to read the SPDs!!!)