Subject: PCFS mount options "noatime"/"atime" [PSARC/2007/415 FastTrack timeout 07/24/2007]
To:      PSARC-record@sac.sfbay.sun.com
Cc:      pcfs-iteam@sun.com
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Case:           PCFS mount options "noatime"/"atime"

Author:         Frank Hofmann

Summary:
        This proposal requests
        * to introduce a mount option pair for PCFS, "-o noatime" resp.
          "-o atime", which suppresses / enables creating access time
          updates.
        * to disable access time updates (use the "-o noatime" option by
          default) for PCFS if it is used on removeable media.

        The Release Binding is patch and the Interface is Committed.

The Problem
        Flash-based removeable media can only perform a limited amount of
        write cycles. In addition to that, writes on such media are very
        slow (compared to reads). Since PCFS is frequently used on such
        devices ("memory sticks"), attempts should be made to minimize
        media write access whenever possible. Access timestamps are an
        easy target for that objective, because:
                - FAT access timestamps are day-granular
                - FAT access timestamps are optional as per FAT spec

        In addition, UFS has had the "noatime" mount option since 1998.
        PCFS should have it as well.

The Proposed Solution
        PCFS will be changed to provide the "atime/noatime" mount options
        just as UFS does via PSARC 1998/093 (RFE 4088189).
        The default behaviour will be different from UFS, though:
                - removeable media:     "noatime" will be default
                - fixed disks:          "atime" will be default
        The reason for that is the abovementioned behaviour of flash devices,
        which are mostly irrelevant for UFS but a main usage scenario for
        PCFS, and the abovementioned behaviour of FAT access timestamps as
        per the specification.

MAN PAGE CHANGES

        The man page for mount_pcfs(1M) will be changed to describe the
        new mount options "atime"/"noatime" as per above (6581003). The
        additional text will be:

                            atime | noatime
                                Enable or disable writing  access
                                timestamps   on   DOS   formatted
                                media.  Default for  fixed  disks
                                is  atime,  while  for removeable
                                media noatime is used. This is so
                                that  writes to flash-based media
                                ("memory sticks") can  be  minim-
                                ized, to prolong lifetime.