Compressed disc image restoration with "threading"

restore.sh

#!/bin/sh

# Assumes images are broken out into 1024mb chunks, separately gzipped, 
# stored as ./image/image.X.blob.gz, where X is an integer (0...).
# Decompresses and writes 6 in parallel (i.e. threading) since Gzip is slow.

DEVICE=$1
sectionsize=1024
maxthreads=5
curthreads=0
set -x
for i in `seq 0 2786`; do 
        blockcount=$(( sectionsize * i ))
        zcat image/image.$i.blob.gz | dd of=$DEVICE bs=1M count=${sectionsize} seek=${blockcount} iflag=fullblock &
        if [ $maxthreads -eq $curthreads ]; then
                curthreads=0
                wait
        else 
                curthreads=$(( curthreads + 1 ))
        fi
done

set +x