Re: 7012-370 Logical Volume

Tim Knight/CT wrote:
> I think I have a great lack of understanding how AIX filesystems work.
> My problem is that I think in terms of DOS and it doesn't apply in the
> same manner.

Tim, I'll try to explain the basics in DOS-like terms to help you out.
I'll take some liberties that would make Uli and other "True Blue" AIX
folks want to scream because important details will be left out or
glossed over, but you can't write the "For Dummies" book and the
"Technical Reference Guide" for the same audience.

AIX wants to refer to your physical hard drives as hdisk0, hdisk1,
etc., similar to how your PC BIOS/DOS interface refers to the first
hard drive as x'80', then x'81', x'82', etc (we're at the FDISK stage
right now, no drive letters yet). In AIX, you create a new volume
group or add the physical hard drive to an existing volume group (In
DOS, you run FDISK and make a primary or extended partition or
partitions). The AIX equivalent of a DOS partition is the logical
volume, once the physical hard drive is assigned to a volume group you
can create one or more logical volumes on the drive.

In DOS, after you create the partition(s) using FDISK, you reboot and
DOS assigns drive letters to the partition(s). In AIX, you create a
filesystem in the logical volume. When you create (or extend) a
filesystem using SMIT(ty), the equivalent of a DOS format is performed
automatically, so at this point the DOS step would be to format the
partition.

OK, so now the DOS drive (C:, for example) is ready to have files
written to it. Not so for AIX, the filesystem must be mounted at a
mount point before it is available for reading/writing. A mount point
is a directory, you can create it yourself or let SMIT(ty) help you do
it, but here's a critical point: Since it is a directory, you can put
files there when the filesystem is not mounted, but those files will
not be visible when you mount the filesystem at the mount point! This
confuses the heck out of non-Unix users and new AIX administrators,
which is why many installations create a directory called /mnt (short
for "mount"), and then create directories under mnt for each device and
"optional" filesystem that might be used, and *never* put files in
those directories. Required filesystems get mounted at system startup,
so manual mounting and unmounting is not needed. So you wind up with
directories like /mnt/cdrom (or sometimes just /cdrom), /mnt/patches,
/mnt/remotefilesystem, etc.

What about that "busy" message on the umount? If any file in a
filesystem is open, AIX will not allow you to unmount that filesystem
(the system is trying to protect your filesystem). One common "open"
file situation is having a terminal session running with the current
directory set to somewhere inside the filesystem. Another common
"gotcha" is running a daemon that has a log file inside the filesystem.

If you are going to have these 2 9GB drives attached all of the time,
I'd suggest having both of them in the rootvg volume group (you could
have 1 in rootvg and the other in another volume group, but that adds a
level of complication that you probably want to avoid). Your fresh AIX
4.3.3 install probably only used one drive (hdisk0), so go ahead and
add hdisk1 to rootvg using SMIT(ty). You'll have lots of unused space
in rootvg, so make a logical volume of a reasonable size (say, 800MB)
and make a filesystem in that logical volume -- use SMIT(ty) for this
task, too. Then mount that filesystem at /usr/sys/inst.images, apply
the maintenance level like IBM wants, and you should be all set. After
everything is done, you could (and probably should) unmount the
filesystem until you have more patches to apply. You could even delete
the logical volume and reclaim the space if you wanted to practice your
filesystem maintenance procedures.

Rick Ekblaw

.

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