#!/bin/bash
# just a script to help with some disk rescue that involves cd writing
# this will output a series of command lines for taking a snapshot of
# a drive or partition, in CD-sized chunks, using dd
#
# edit these to suit
    # disk info in MB, where 1MB = 1024*1024 bytes = 1048576 bytes
    # get diskend by:
    #  'fdisk -lu' which will show sectors of 512 bytes
    #  'echo "scale=1;([end sector] - [start sector])/2048" | bc
    #  the 2048 comes from: (512 bytes per sector) / (1024 * 1024) bytes per Mb
    #  round the result up to the nearest integer for $diskend
        diskend=24380
    # $chunk is the size of the CD, in Mb
        chunk=660
    # which disk
        disk=/dev/hda12
    # get a name for dd's output, tail of $disk above,
    # to be combined with the count later
        fname=${disk##*/}
    # blocksize, in bytes, used in dd
    # 1MB (1024 * 1024) is chosen here
        block=1048576

# bytes in a sector
sector=512
# sectors per block
secb=$((${block} / ${sector}))
numchunks=$(($(echo "${diskend} / ${chunk}" | bc ) + 1))
# counters
skip=0
cnt=0
while [ ${cnt} -lt ${numchunks} ]
do
    start=$((${cnt} * ${chunk}))
    end=$((${start} + ${chunk}))
    if [ ${end} -gt ${diskend} ]
        then
            chunk=$((chunk - (${end} - ${diskend})))
            end=$((${diskend}))
    fi
    fpre=$((${cnt}+1))
    if [ ${fpre} -lt 100 ]
        then
            fpre=0${fpre}
    fi
    if [ ${fpre} -lt 10 ]
        then
            fpre=0${fpre}
    fi
    secst=$((${start} * ${secb}))
    secen=$((${end} * ${secb}))
    echo "dd if=${disk} of=${fpre}${fname} bs=${block} skip=${skip} count=${chunk}"
    echo "			(start=${start}MB, ${secst}s,  end=${end}MB, ${secen}s)"
    skip=$((${skip} + ${chunk}))
    cnt=$((${cnt} + 1))
done
echo "chunks=${numchunks}"