How much space do I need to create a backup with fsdisk

Question

I get this error when mounting a drive

[ 4337.380506] EXT4-fs (sda): bad geometry: block count 156282966 exceeds size of device (156282701 blocks)

So if I try to fix it with sfdisk do I need space for the entire drive (640gb) or just as much as the data that is on the disk contains? (about 400gb)

backup like so

sfdisk -d /dev/sda > PT.txt

I'm trying to follow this help here - http://ubuntuforums.org/showpost.php?p=9485779&postcount=7

Answer 1

Hmm. I've never tried to recover from such a situation. However, if you've got valuable data on that disk, I strongly recommend making a complete image of the disk before doing anything else. That means you'll need a device with at least as much free space as your disk has. Then do

dd if=/dev/sda of=/path/to/image.img

That way, if something goes wrong, you won't lose anything.

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If you don't have enough space on a single partition, you might be able to work around that issue by doing something like this (WARNING: This is untested):

mkfifo /tmp/dd
dd if=/dev/sda of=/tmp/dd

Then, in another terminal, try this

split --bytes=4G /tmp/dd /path/to/staging/area # adjust size as appropriate

Finally, in a third terminal, you can quickly move the chunks to their permanent home, optionally compressing them first. Do this while dd runs. But whatever you do, make sure it's fast enough so that you don't run out of space in the staging area.

To restore the split files, you can do something like this:

Terminal 1:

mkfifo /tmp/dd
cat /path/to/chunks/dir/1/* /path/to/chunks/dir/2/* > /tmp/dd # List all chunks here

Use zcat instead of cat if you also need to uncompress the chunks.

Terminal 2:

dd if=/tmp/dd of=/dev/sda