At the risk of mixing this pot up more, I think I understand the confusion that is going on here in AFS land about SGI and sparse files. FYI, Masscomp (aka Concurrent), was the first to support ``extent based file systems'' for UNIX -- with Stellar and SGI also later supporting them (in 1981). These are also called ``real-time'' or ``contiguous files'' because they lay the file down in contiguous areas of the disks. They are different from traditional UNIX file systems, in that perform better (that is usually reasonably easy) and predictably (very hard). While Masscomp did not allow true extents for all files (like Stellar and SGI), sparse files are not allowed in contiguous files of any of the extent based systems. The reason is that during rewrite of the file, if you allowed sparse layout, you would lose the performance and >>predicable<< behavior needed and required by those systems. Anyway, in the mid-1980's SGI wrote their ``EFS'' - extent based file system. I believe there is a USENIX paper, althought the paper I read years ago may have been an SGI ``white-paper'' and never published. Thus sparse files went away for SGI with the introduction of an extent base FS. Other UNIX systems which still use the V7 or BSD (aka UFS) file systems offer sparse files (which save on-disk space). I'm not sure what Veratas does in this area? Anybody know? Clem Cole Sr. Scientist Locus Computing Corp
