Very Computer

I just hosed the /usr partition on an RS/6000 (530, AIX 3.1.7).
How?  I am still not sure!!!  But that comes later, because what
I want to do  is fix the thing first.

I was trying to incease the size of the partition using smit,
and I am kind of hazy on the details after that (should take a
look at the smit.log file, but only if I can get the danged thing
fixed first). Anyway, I killed the superblock on the partition.

I thought that I could boot up in single user mode, mkfs on /dev/hd2
(which is where /usr was mounted from), and restore from another
RS/6K machine.  But was I mistaken.  The manual starts talking about
volume groups and varyoff and varyon on the vg's etc.  I thought that
I was following all that, except the manual does not talk of partitions
(with the mkdev command), only physical disks.  I would go back into
smit, but the terminal is all screwed up (cannot use the up/down arrow
keys after I booted from the floppies), and that makes smit useless
too.

Help!!! All I want to do is mkfs on /dev/hd2 and I then hopefully
can get the lpp's and other stuff back (and life will be fun).
How?

Thanks,
Deepak Narain

Yesterday I posted a thingy describing a problem that I had
after I hosed the /usr partition, and couldn't mkfs it in single
user mode.  Anyway, I fixed that problem.  (after lots of pain
too, I might add).  Anyway, now here's another question:

Aren't the /dev/hd? that are made in the installation process
logical volumes?  If not, why  bother not naming them lv?? (which
is what crfs does by default).  I did a file on one of the
/dev/hd? and the /dev/lv?? files and both of them have the same
major device id, only different minor device id's.  Which leads
me to think that they might be the same.  Am I right/wrong/ignorant
here.  Please let me know either way.

Thanks,
deepak narain

In AIX, filesystems and logical volumes are not the same...in fact, are only
faintly related.  Filesystems are not radically different from vanilla unix,
but the logical volume manager (LVM) is a breed unto itself.  You asked if
/dev/hd? are the logical volumes...not exactly.  They are, as you pointed
out, devices to *access* the logical volumes.  Perhaps it will help if you
think of logical volumes as "partitions" (term we used with System V) of the
actual, physical hard disk(s).  The beauty of the LVM is its easy extensibility.Yesterday I "glued" an extra 3 PPs (physical partitions in AIXspeak) onto
an existing filesystem without having to stop anybody from working.  On one
of my SysV boxes, that would have meant dismounting the f/s and running it
off to tape, followed by re-partitioning (and possibly reformatting) the disk,
followed by a restore of the tape.  Being able to just "slap 12 meg onto the
end of a filesystem like a lump of play-doh" saved me hours of time.

If you have access to it, there is a pretty fair explanation of the LVM in
"General Concepts & Proceedures", IBM part # SC23-2202-00.

oz

...

Quote:>Aren't the /dev/hd? that are made in the installation process
>logical volumes?  If not, why  bother not naming them lv?? (which
>is what crfs does by default).  I did a file on one of the
>/dev/hd? and the /dev/lv?? files and both of them have the same
>major device id, only different minor device id's.  Which leads
>me to think that they might be the same.  Am I right/wrong/ignorant
>here.  Please let me know either way.

In a word - history.  The conventional naming of the "disk devices" in
RT AIX was /dev/hd...  These names where retained in AIX V3.  So the
install code specifies those names for the logical volumes it creates.
If you create logical volumes, their default names are of the form
/dev/lv..., but you can specify any device names you like.

The logical volume device model uses a major number for each volume
group, and a minor number for each logical volume in that volume group.
--

The hd? names are logical volumes, but the names are left-overs
from the RT days (I think).  All the "system" logical volumes are
called "hd1, hd2.....".  mklv (which crfs calls) will use a
default prefix of "lv" when it create logical volumes, unless
you specify a name with the -y flag.

The reason the hd's and the lv's have the same major numbers is
because they are all in the same volume group.  The volume group is
the device that gets the major number in the kernel, and each lv
has it's own minor number.  

Later,
Julie
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IBMNET: JULIEL at AUSVMQ 2F-007/903  (512) 838-2677 (Tie 678-2677)
"I'm not getting defensive!"