- Make a partition that is at least as big as your first partition
was. You can make it larger than the original partition by any
amount. If you underestimate, there will be much wailing and
gnashing of teeth.
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-23361, default 1): <RETURN>
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-22800, default 22800): 13032
Command (m for help): w
- Run dumpe2fs on the first partition and grep out the block count
Example:
% dumpe2fs /dev/sda1 | grep "Block count:"
Block count: 41270953
If you are uncertain about this value, repeat Step 1 with a
bigger partition size. If the block count changes, then you
underestimated the size of the original partition when you made
your first guess. Repeat Step 1 until you get a stable block
count.
- Remove the partition you just created
Command (m for help): d
Partition number (1-4): 1
- Make a new partition with the exact size
you got from the block count. Since you cannot enter block size in
fdisk, you need to figure out how many cylinders to
request. Here is the formula:
(number of needed cylinders) = (number of blocks) / (block size)
(block size) = (unit size) / 1024
(unit size) = (number of heads) * (number of sectors/cylinder) * (number of bytes/sector)
Consider the following example, where a hard drive has been
partitioned into four primary partitions
of 1, 2, 4, and 8 cylinders.
disk /dev/sda: 16 heads, 63 sectors, 23361 cylinders
Units = cylinders of 1008 * 512 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 2 976+ 83 Linux
/dev/sda2 3 5 1512 83 Linux
/dev/sda3 6 10 2520 83 Linux
/dev/sda4 11 19 4536 83 Linux
fdisk provides the configuration information I need in
the head of the output.
The unit size is 516096 ( 16 heads * 63 sectors/cyl * 512
bytes/sector ).
The block size is 504 ( 516096 / 1024 ).
The number of needed cylinders for the second partition is therefore
3 ( 1512 blocks / 504 ).
The partition table shows that this is indeed the case: the
first cylinder is 3, the second 4, and the last is 5, for a total of
three cylinders.
The number of needed cylinders for the third partition is calculated
similarly: 2520 blocks / 504 = 5, which corresponds to
10 - 6 (plus one, since we are counting the 6th through the
10th cylinders inclusively).
Notice that this calculation does not work for the first partition
because the block count is wrong ( 976 instead of 1008 ). The plus sign
indicates that not all the blocks are included in the fdisk
value. When you try the calculation ( 976 / 504 ) you get 1.937. Knowing
that the number of cylinders must be an integer, you can simply round up.
- Run e2fsck on it to verify that you can read the new partition.
- Repeat Steps 1-5 on remaining partitions.
