johnl (12/02/82)
Dan Ts'o asks whether the Unix disk cache still makes a big performance difference since most programs use stdio which reads and writes full blocks. The answer appears to be emphatically yes, for two reasons. One is that the read-ahead and write-behind aspects of the disk cache account for most of the I/O overlap that you get. The more important reason is that there are disk blocks that get read over and over again, most notably directories in many search paths. We did some monitoring and found that with enough buffers, 70-80% of disk reads are satisfied from stuff already in memory. John Levine, IECC, PO Box 349, Cambridge MA 02238; (617) 491-5451 decvax!yale-co!jrl, harpo!esquire!ima!johnl, ucbvax!cbosgd!ima!johnl (uucp) Levine@YALE (Arpa).