OBERMAN@ICDC.LLNL.GOV ("Kevin Oberman, LLNL, 422-6955, L-156", 415) (05/16/88)
>For archiving purposes, you don't need to keep close track of the last >access time; you need a resolution equal to how long it can be since a file has >been accessed before you want to archive it. This can be done by setting >the retention period on the volume (on CITHEX, this is 6 months minimum, 6 >months and a day maximum). Carl is right about the viability of retention time for keeping track of access for archive reasons, but I wonder about his selection of times. Six months is as reasonable as anything, but a single day from minimum to maximum stikes me as just a bit low. The reason VMS uses retention time as opposed to a last access time is to reduce the overhead of constantly updating file headers. By using a min-max system, the header only needs to be updated when its expiration date crosses the min-max boundry. If the difference is one day, the headers need to be updated every day the file is accessed, though not for subsequent accesses on the same day. This represents a small, but significant overhead. It also means that you know the EXACT date (but not time) of the last access. In Carl's case he can just take the expiration date and subtract 180 days. Since retention time is specified in days, I'm guessing that Carl assumed 30 day months. However, if the only reason for keeping track of last access is archiving, then I would recommend a span of about a week between min and max. Say a 180 day minimum and a 187 day maximum. This provides a knowledge of which week the file was accessed, but requires that headers on read-only file be updated only one a week at the most. I guess the jist of this is that by setting a small min-max retention time window you can have an effective "last access date" or with a larger window, a reasonable period for archiving at a cost of higher system overhead. In either case I would find it hard to justify the overhead of an access time that is updated every time a file is accessed. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything.