Adding more space
This article is fairly specific to SCO Unix, but the general
concepts of moving data and creating a symbolic link do apply to any Unix and Linux.
Sooner or later it happens: you type "df -v" and see that the
"%used" is pushing 99%. Or, worse, you get awful messages on the
console: No space on device 1/40.
(If you are out of space right now, follow this link for
suggestions as to what to do right
So, it's time to add more disk space. There are two basic ways
to approach this problem. You could replace the current disk with
something larger, or simply add another disk. Both methods have
their own positive and negative aspects. Let's consider some of
Replace the current disk
This can be the simplest solution of all, particularly if you
are using emergency boot and recovery disks such as can be made by
Microlite Edge or other
similar products. Do a backup, pop out the old disk, in with the
new, boot with the Recovery disks, and very quickly you have a
Another way to do that is detailed at Transfer data and make bootable secondary (SCO Unix).
But this assumes that you either have some other use for your
current disk, or that it's old and worthless enough that you are
willing to toss it out. That may be the case, but in those
situations, you may have a further problem if you have to replace
the old disk with a different architecture. You may have an old IDE
disk, and want to replace it with a new SCSI Raid system, for
example. In those situations, the Emergency Recovery disks may not
be enough, and you may have to start with a fresh install of the OS
and proceed from there.
Add another disk
Adding storage can, of course, involve similar trade-offs. You
could add a SCSI drive to an existing IDE drive, for example, but
generally not vice-versa. You also need to decide what information
you are going to store on that new space, and how you are going to
get it there. Some programs have the ability to make use of new
space fairly simply, but more often than not, you are going to have
to do some data rearranging.
See Adding a disk
drive for details on how to add the disk
Dividing the disk
Whichever way you decide to go, you need to start thinking about
partitions before you do anything. Partitions, as you may now, are
the areas that your hard drive is divided into. It can be a little
confusing, because there are really two kinds of divisions: "fdisk"
partitions and "divvy" partitions (which are called "divisions" by
SCO, but "partitions" by some other Unixes, which is why it gets
If you have an older version of SCO, you may have to be
concerned about fdisk partitions for very large drives. More modern
versions are able to support about anything you could conceivably
purchase (assuming proper drivers, of course). If you have SCO
3.2v4.2, you will probably need or want uod429a for EIDE or
large SCSI drives. This supplement has some confusing aspects to
it, so read the README file carefully and completely.
I'll assume for the moment that you have no issues that cannot
be resolved by proper drivers or supplements, and that you will be
creating one Unix fdisk partition. It's now time to think about
These divisions divide your Unix partition into filesystems or
raw disk partitions. Raw partitions are strictly for the use of
programs like Informix that are written to use these partitions,
generally to obtain higher performance. Without such programs, your
divisions will be used for ordinary Unix filesystems. Older systems
usually had just a root division or possibly a root and a /u
(The "root" division is the one that shows up as "/" mounted on
"/dev/root"). Release 5 systems usually have a root and a small
/stand. You need to decide what partitions you will create,
and how large they will be.
On older releases, the OS constrains your choice to some degree
because 3.2v4.2 and below simply cannot handle a filesystem larger
than 2 gigabytes. If you had a raw partition, that could be larger,
but any filesystem prior to 3.2v5.x has to be 2 gigabytes or
Assuming Release 5, or a 4.2 system with a 2 gig drive, why not
dispense with extra divisions and simply have one large file
You could do that. With release 5, you'll probably still want a
small (15-20MB) /stand filesystem, because Unix can't boot from an
HTFS filesystem, and that's what you would want the root to be. The
/stand would be an (older) EAFS filesystem, which Unix can boot
from, and the root would be the higher performance and more
reliable HTFS type.
Even on 3.2v4.2, you could have one large root filesystem (up to
2 gigabytes). It's very convenient to do this; you don't have to
worry about how much space to allocate to what, you just let the
whole disk be one big filesystem.
For several reasons, you probably don't want to do that. On the
older releases (and even on the newer, under some conditions), big
file systems can take a long time to clean and repair in the event
of an unexpected crash. It is also true that damage to a hard drive
usually confines itself to one file system. In other words, if a
defective hard drive trashes your root filesystem, a separate /u
file system may escape damage entirely. This can make recovery
simpler and more complete, because the data on /u may be current
right up to the crash.
Deliberately limiting space
You may also want to create file system divisions to
specifically limit how much space can be used. At first, this may
seem silly, but consider the often seen case where a naive user
keeps submitting the same large print job over and over, not
understanding that it is not printing for some other reason
(printer offline?) and that each submission is using up more disk
space. Consider also a runaway program that keeps creating a larger
and larger file. Wouldn't it be nice to let a separate file system
run out of space before the whole drive is used up? In the case of
the printing, you could create a small division and mount it at
Note that you have to be a little bit careful about creating
partitions that will be used for system directories, like
/user, and on Release 5, the mess of symbolic links means
you have to tread even more carefully. With enough care and
forethought, you can do whatever you need to do. You have to
watch out for things that need to be present when the system is
booting; if you are planning on moving anything like that
elsewhere, you will have to leave some of it behind, ultimately to
be hidden beneath your new file system. This can get tricky, so be
careful or hire competent help.
Deciding what to move
You may have one large area that will continue to grow. For
example, /usr/mas90, /appl/filepro, and /usr/rwc65 are common SCO
programs that have defined directory structures. If you have or can
identify such an area, then this is the data you will move.
You may, however, have two or more areas to move. You can solve
this by creating multiple file systems in the new space, or by
using one file system and symbolic links to point to the new data
There are things you cannot move. You cannot, for
example, move /usr or any part of it that needs to be present as
the machine boots or in single user mode. DO NOT MOVE ANYTHING THAT
ISN'T YOURS and you'll be safe.
If you are installing a replacement drive, you are not concerned
with moving data. If, for example, your old system had a large
/data filesystem, you could simply specify a larger division when
divvy'ing the new disk. The restore will simply put the old data in
the new, larger, division.
But when adding a new hard drive, you may want to move the
contents of a directory to the new space. The following procedure
Create the new space with "mkdev hd" as required. Relink, and
reboot. Rename the directory you are going to move, using the "mv"
command. For example:
mv /usr/data /usr/data.safe
Note the ownership and permissions of /usr/data.safe, and create
a new /usr/data directory with the same permissions and ownership.
# cd /usr
# mv data data.safe
# ls -ld data.safe
drwxr-xr-x 2 root sys 512 Nov 16 18:47 data.safe
# mkdir data
# chown root data
# chgrp sys data
# chmod 755 data
# ls -ld data
drwxr-xr-x 2 root sys 512 Nov 16 18:47 data
Run "mkdev fs", giving the name of the directory you want to
move as the mount point (/usr/data). Then type:
mountall to mount the new space at /usr/data (or
simply type "mount /usr/data").
Type the following to copy the data:
# cd /usr/data.safe
# find . -depth -print | cpio -pdlmv ../data
After this is done, and you are completely satisfied that
everything is working as it should be, you can "rm -r
If you are using symbolic links, the procedure is similar.
First, create a new directory on the other drive:
Assign appropriate permission to
Copy the data as before, and mv the oldname aside:
find . -depth -print | cpio -pdlmv /bigdrive/newdata
mv /usr/data /usr/data.sf
Now create the symbolic link:
ln -s /bigdrive/newdata /usr/data
Again, when you are satisfied that everything is working, come
back and "rm -r /usr/data.safe".
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© 2012-12-17 Tony Lawrence