lmb@vicom.com (Larry Blair) (06/13/89)
In Sun-Spots v7n303 I wrote about some testing that I did for optimization. Thanks to Art Hays <lsr-vax!art@uunet.uu.net>, I found that the results that I published were incomplete and that there is a bug in BSD 4.2 and 4.3 (including all levels of SunOS) that prevents changing the maxcontig parameter of the filesystem ("tunefs -a 16") from working properly. While changing maxcontig will eliminate the insertion of rotational delays in the indirect blocks of a large file, it does not cause the blocks directly accessed through the inode to be contiguous. The use of "tunefs -d 0", which is recommended by the controller manufacturers, does properly remove the rotational delays. My performance tests were performed with a few, very large, files. The ratio of direct to indirect blocks was low enough to not affect the times appreciably. Retesting with many 90K files (the largest file that doesn't use indirect blocks) shows the problem. Reading through an od of the filesystem reveals the bug. Larry Blair ames!vsi1!lmb lmb@vicom.com