Lecture 29

Access to Floppy Disk Filesystems

Although you can place some interesting filesystem on a floppy disk, there's generally no reason to do so. Instead, most people want to get to the floppy disk as if it is a DOS filesystem.
Different systems provide this capability in different ways.
Solaris and IRIX have floppy device daemons that broker access to the floppy device. Sun uses executables like volcheck (to create a DOS filesystem for a floppy in the drive), fdformat (to format a disk), and eject to unmount the drive. Unmounting is the weak link in this system. Users don't do it.
AIX provides the (weak) tools dosdir, dosformat, dosread (to copy from DOS disk), doswrite (to copy to DOS disks), and doscel.
More portable is the mtools package available from http://www.tux.org/pub/tux/knaff/mtools/index.html.
This is a highly portable set of tools that can be configured for practially any system.
Get, make it, and depotize it.

Logical Volume Managers

Why even have logical volumes?

Dealing with the specific physical details of disks is just a nightmare. When you install a system that requires physical partitioning of the disk, you're require in advance and determine how much space you want for various activities. Instead, why not allocate the minimum necessary space, then allow the partitions to grow as necessary? That's exactly what logical volumes allow you to do.

And suppose our partition grows too big to fit on one disk? Why not allow it to span across multiple disks? That's another capability logical volumes support.

There is some nomenclature that's associated with logical volume managers, and there is some disagreement about what terms should be used for which concepts. You may find other names than the ones that follow being used for the same things.

A physical volume is a disk
A physical volume group is a named collection of disks.
A logical volume is a portion of a physical volume group upon which a filesystem and be created. Their size can be easily increased after creation.
Creation of a logical volume can specify such functional properties as mirroring and striping.
HP-UX and Digital Unix make it easy to reduce the size of a logical volume with lvreduce. Not AIX :-(
To reduce the size of an AIX filesystem, you must back it up, delete it and its logical volume, create a new smaller logical volume, then restore the files on the filesystem.
This is exactly what you'd do with a physical filesystem manager.
AIX Management utilities:
- lsdev -C -c disk: list the disks on the system
- mkvg -y "volume-group-name" hdiskm hdiskm
  Use -s to specify size in MB.
- varyonvg volume-group-name: activate a volume group
- extendvg volume-group-name hdiskp: Extend volume group to include a new disk.
- chvg: change characteristics of a volume
- reducevg: remove a disk from a volume group
- importvg: Add existing volume group to system
  exportvg: Remove a volume group but don't alter it
  These are used to move disks between one system and another.
- mklv -y "lvname" volgrp n [disks]: Make a logical volume. n is number of logical partitions (4 MB blocks).
- mklv -y cdata -S 64K chemvg 125 hdisk5 hdisk6
  -S tells stripe size