Lost disk space

[Paul Campbell]

In article <1990Oct11.162202.17099 at wdl1.wdl.fac.com> tpm at wdl58.wdl.fac.com (Tim P McNerney) writes:
>
>We have a hard disk in which the partition size and the file size do not
>correspond.  To be more specific, our 156MB A/UX partition was made into
>a 78MB file system (using mkfs) and was not caught for some time.
>
>Is there some way in which to non-destructively remake the file system so
>as to regain the missing 78MB?  If not, any suggestions on how to save the
>missing 78MB?

The following trick can be used to do this - be warned, if done wrong
it can trash your disk!!

I'm assuming that you really did make the file system with mkfs or mkfs1b
and NOT with newfs (ie it's a System V file systems and not a Berkeley
Fast File System - if you are running 2.0, now might be a good time to
back everything up, build a FFS and do the conversion).

Before you start un mount the file system

Anyway, you have to figure out how big the new file system will be in
LOGICAL blocks (if you used mkfs to build your disk a logical block is
2 physical blocks, if you used mkfs1b the relationship is 1 to 1).
As root you can find out how big the file system thinks it is, try
as root:

	adb -k /dev/dsk/c1d0s0		< or what ever you disk partition is
	202?D
	^D

The second line should print out the number of LOGICAL blocks, if
you used mkfs then for 78Mb it's going to be something around 78000,
if you used mkfs1b it will be near 156000. Figure out how many LOGICAL
blocks you really want the file system to have (in your case you probably
just double the number - check out the partition table using dp to get
the number of physical blocks [the term 'logical' blocks in dp is different
from LOGICAL blocks referenced by filesystems so don't get confused]).
Assuming you got a number of 12345 for the new size (in LOGICAL blocks) for
your filesystem here's how you change it (the dangerous part), as root type:

	adb -k -w /dev/dsk/c1d0s0	< or what ever your disk partition is
	202?W 0d12345			< or your LOGICAL block count
	^D

Now you have hacked the super-block on the file system, to repair the free
block list enter:

	fsck /dev/rdsk/c1d0s0		< or what ever your disk partition is

It will tell you that there are blocks missing from your free block list
and ask if you want to rebuild it, answer 'y' to this question. After the
free block list has been rebuilt you are done and can mount your new 
bigger filesystem again.

BTW: if you have a system where you take it down often and always check
the (System V filesystem only) disks on the way back up enter '-s' to the
fsck line, this forces the filesystem's free list to be re-ordered - something
that is worth doing on a filesystem fairly often to give you a small increment
in performance.

	Paul Campbell
	Taniwha Systems

-- 
Paul Campbell    UUCP: ..!mtxinu!taniwha!paul     AppleLink: CAMPBELL.P
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