Amanda doesn't actually handle reading the files; it uses dump
(available on BSD and traditional unixes) and GNU tar (available pretty
much everywhere) to read files and make a dump stream.

I'm not sure if you're asking about a problem where some methods skip
files that are currently open, issues with getting an atomic snapshot,
or something more complicated about files that are being written.

I'm not sure about VSS, but fss is a term in NetBSD for taking snapshots
of filesystems so that dump and tar can get consistent views.  Other
UNIX-like systems have similar features.  I would expect that a feature
like this is available on Macs, and I don't know about windows.



FSSCONFIG(8)            NetBSD System Manager's Manual            FSSCONFIG(8)

NAME
     fssconfig -- configure file system snapshot devices

SYNOPSIS
     fssconfig [-cxv] device path backup [cluster [size]]
     fssconfig -u [-v] device
     fssconfig -l [-v] [device]

DESCRIPTION
     The fssconfig command configures file system snapshot pseudo disk
     devices.  It will associate the file system snapshot disk device with a
     snapshot of path allowing the latter to be accessed as though it were a
     disk.

     If backup resides on the snapshotted file system a persistent snapshot
     will be created.  This snapshot is active until backup is unlinked.  This
     snapshot mode is only supported for ffs files systems.

     Otherwise data written through the path will be saved in backup.  If
     backup is a regular file, it will be created with length size.  Default
     size is the size of path.  Data is saved to backup in units of cluster
     bytes.

     Options indicate an action to be performed:

     -c   Configures the device.  If successful, references to device will
          access the contents of path at the time the snapshot was taken.  If
          backup is a directory, a temporary file will be created in this
          directory.  This file will be unlinked on exit.

     -l   List the snapshot devices and indicate which ones are in use.  If a
          specific device is given, then only that will be described.

     -u   Unconfigures the device.

     -v   Be more verbose listing the snapshot devices.

     -x   Unlink backup after the device is configured.

     If no action option is given, -c is assumed.

FILES
     /dev/rfss?
     /dev/fss?

EXAMPLES
           fssconfig fss0 /usr /tmp/back

     Configures the snapshot device fss0 for a snapshot of the /usr file sys-
     tem.  Data written through /usr will be backed up in /tmp/back.

           fssconfig fss1 / /dev/rsd0e 8192

     Configures the snapshot device fss1 for a snapshot of the / file system.
     Data written through / will be backed up in /dev/rsd0e.  The backup will
     take place in units of 8192 bytes.

           fssconfig -u fss0

     Unconfigures the fss0 device.

SEE ALSO
     opendisk(3), fss(4), mount(8), umount(8)

HISTORY
     The fssconfig command appeared in NetBSD 2.0.

BUGS
     The fss(4) driver is experimental.  Be sure you have a backup before you
     use it.

NetBSD 4.0_RC1                 January 31, 2005                 NetBSD 4.0_RC1