In Message <Pine.NEB.3.96.981119013741.6871B-100000@dream.future.net> ,
   "Tom T. Thai" <tomthai@future.net> wrote:

=>Do we have something like the following?
=>
=>"AIX has had a Journaled file system for years - just add a hot swap
=>SCSI disk or SSA disk, give it to the volume group containing the
=>database and expand the filesystem - all while the system is running."

   Having had some experience with AIX, this is in fact a very nice
feature to have, and we don't have anything like it in NetBSD that
I know of.
   There are actually two pieces here: The logical volume manager
and the JFS. JFS, as I understand it, is your basic FFS at its
core, but adds a partition which logs metadata writes and the
ability to grow the file system while it is in operation. The LVM
introduces two abstractions: the volume group, which combines disks
into a sort of logical disk, and logical volumes, which are like
a logical partition. Each logical volume lives in a single volume
group, possibly spanning multiple physical disks. To the OS, a
logical volume acts like a partition, so it can be used through a
raw device, have a JFS created on it, etc. Since the VG/LVs are
fairly abstract, you can grow them by simply adding disks to the
VG, which just adds a bunch of blocks to allocate from, or extend
the LV by allocating more blocks from the VG to tack onto the end.
The latter is used when growing JFSs; the JFS layer just has to be
told that it has a larger logical volume than it used to to do its
thing.
   Very nice to have, and it would be an interesting project to
add support for it to NetBSD.

                                      Gary D. Duzan
                         Humble Practitioner of the Computing Arts