diff --git a/src/disk.sh b/src/disk.sh
index 0ff2928..6a02394 100644
--- a/src/disk.sh
+++ b/src/disk.sh
@@ -4,18 +4,18 @@ set -Eeuo pipefail
 # Docker environment variables
 
 : ${DISK_IO:='native'}    # I/O Mode, can be set to 'native', 'threads' or 'io_turing'
+: ${DISK_FMT:='raw'}      # Disk file format, "raw" by default for backwards compatibility
 : ${DISK_CACHE:='none'}   # Caching mode, can be set to 'writeback' for better performance
 : ${DISK_DISCARD:='on'}   # Controls whether unmap (TRIM) commands are passed to the host.
 : ${DISK_ROTATION:='1'}   # Rotation rate, set to 1 for SSD storage and increase for HDD
-: ${DISK_FMT:='raw'}      # Disk file format, "raw" by default for backwards compatibility
 
 DISK_OPTS=""
 BOOT="$STORAGE/boot.img"
 
 if [ -f "$BOOT" ]; then
-  DISK_OPTS="${DISK_OPTS} \
+  DISK_OPTS="$DISK_OPTS \
     -device virtio-scsi-pci,id=scsi0 \
-    -drive id=cdrom0,if=none,format=raw,readonly=on,file=${BOOT} \
+    -drive id=cdrom0,if=none,format=raw,readonly=on,file=$BOOT \
     -device scsi-cd,bus=scsi0.0,drive=cdrom0,bootindex=10"
 fi
 
@@ -30,7 +30,7 @@ fmt2ext() {
       echo "img"
       ;;
     *)
-      error "Unrecognized disk format ${DISK_FMT}" && exit 88
+      error "Unrecognized disk format: $DISK_FMT" && exit 88
       ;;
   esac
 }
@@ -46,7 +46,7 @@ ext2fmt() {
       echo "raw"
       ;;
     *)
-      error "Unrecognized file extension .${DISK_EXT}" && exit 90
+      error "Unrecognized file extension: .$DISK_EXT" && exit 88
       ;;
   esac
 }
@@ -57,17 +57,17 @@ getSize() {
   local DISK_FMT
 
   DISK_EXT="$(echo "${DISK_FILE//*./}" | sed 's/^.*\.//')"
-  DISK_FMT="$(ext2fmt "${DISK_EXT}")"
+  DISK_FMT="$(ext2fmt "$DISK_EXT")"
 
   case "${DISK_FMT,,}" in
     raw)
-      stat -c%s "${DISK_FILE}"
+      stat -c%s "$DISK_FILE"
       ;;
     qcow2)
-      qemu-img info "${DISK_FILE}" -f "${DISK_FMT}" | grep '^virtual size: ' | sed 's/.*(\(.*\) bytes)/\1/'
+      qemu-img info "$DISK_FILE" -f "$DISK_FMT" | grep '^virtual size: ' | sed 's/.*(\(.*\) bytes)/\1/'
       ;;
     *)
-      error "Unrecognized disk format: ${DISK_FMT}" && exit 88
+      error "Unrecognized disk format: $DISK_FMT" && exit 88
       ;;
   esac
 }
@@ -76,6 +76,7 @@ resizeDisk() {
 
   local GB
   local REQ
+  local FAIL
   local SPACE
   local SPACE_GB
   local DISK_FILE=$1
@@ -86,42 +87,44 @@ resizeDisk() {
   local DISK_FMT=$6
 
   GB=$(( (CUR_SIZE + 1073741823)/1073741824 ))
-  info "Resizing ${DISK_DESC} from ${GB}G to ${DISK_SPACE} .."
+  info "Resizing $DISK_DESC from ${GB}G to $DISK_SPACE .."
+  FAIL="Could not resize $DISK_FMT file of $DISK_DESC ($DISK_FILE) from ${GB}G to $DISK_SPACE .."
+
+  REQ=$((DATA_SIZE-CUR_SIZE))
+  (( REQ < 1 )) && error "Shrinking disks is not supported!" && exit 84
 
   case "${DISK_FMT,,}" in
     raw)
-      if [[ "${ALLOCATE}" == [Nn]* ]]; then
+      if [[ "$ALLOCATE" == [Nn]* ]]; then
 
         # Resize file by changing its length
-        if ! truncate -s "${DISK_SPACE}" "${DISK_FILE}"; then
-          error "Could not resize ${DISK_DESC} file (${DISK_FILE}) to ${DISK_SPACE} .." && exit 85
+        if ! truncate -s "$DISK_SPACE" "$DISK_FILE"; then
+          error "$FAIL" && exit 85
         fi
 
       else
 
-        REQ=$((DATA_SIZE-CUR_SIZE))
-
         # Check free diskspace
-        SPACE=$(df --output=avail -B 1 "${DIR}" | tail -n 1)
+        SPACE=$(df --output=avail -B 1 "$DIR" | tail -n 1)
         SPACE_GB=$(( (SPACE + 1073741823)/1073741824 ))
 
         if (( REQ > SPACE )); then
-          error "Not enough free space to resize ${DISK_DESC} to ${DISK_SPACE} in ${DIR}, it has only ${SPACE_GB} GB available.."
+          error "Not enough free space to resize $DISK_DESC to $DISK_SPACE in $DIR, it has only $SPACE_GB GB available.."
           error "Please specify a smaller ${DISK_DESC^^}_SIZE or disable preallocation by setting DISK_FMT to \"qcow2\"." && exit 84
         fi
 
         # Resize file by allocating more space
-        if ! fallocate -l "${DISK_SPACE}" "${DISK_FILE}"; then
-          if ! truncate -s "${DISK_SPACE}" "${DISK_FILE}"; then
-            error "Could not resize ${DISK_DESC} file (${DISK_FILE}) to ${DISK_SPACE}" && exit 85
+        if ! fallocate -l "$DISK_SPACE" "$DISK_FILE"; then
+          if ! truncate -s "$DISK_SPACE" "$DISK_FILE"; then
+            error "$FAIL" && exit 85
           fi
         fi
 
       fi
       ;;
     qcow2)
-      if ! qemu-img resize -f "${DISK_FMT}" "${DISK_FILE}" "${DISK_SPACE}" ; then
-        error "Could not resize ${DISK_DESC} file (${DISK_FILE}) to ${DISK_SPACE}" && exit 85
+      if ! qemu-img resize -f "$DISK_FMT" "$DISK_FILE" "$DISK_SPACE" ; then
+        error "$FAIL" && exit 85
       fi
       ;;
   esac
@@ -129,25 +132,26 @@ resizeDisk() {
 
 convertDisk() {
 
-  local CONV_FLAGS=""
+  local CONV_FLAGS="-p"
   local SOURCE_FILE=$1
   local SOURCE_FMT=$2
   local DST_FILE=$3
   local DST_FMT=$4
 
-  case "${DST_FMT}" in
+  case "$DST_FMT" in
     qcow2)
-      CONV_FLAGS="${CONV_FLAGS} -c"
+      CONV_FLAGS="$CONV_FLAGS -c"
       ;;
   esac
 
   # shellcheck disable=SC2086
-  qemu-img convert ${CONV_FLAGS} -f "${SOURCE_FMT}" -O "${DST_FMT}" -- "${SOURCE_FILE}" "${DST_FILE}"
+  qemu-img convert $CONV_FLAGS -f "$SOURCE_FMT" -O "$DST_FMT" -- "$SOURCE_FILE" "$DST_FILE"
 }
 
 createDisk() {
 
   local GB
+  local FAIL
   local SPACE
   local SPACE_GB
   local DISK_FILE=$1
@@ -155,40 +159,43 @@ createDisk() {
   local DISK_DESC=$3
   local DISK_FMT=$4
 
+  FAIL="Could not create a $DISK_SPACE $DISK_FMT file for $DISK_DESC ($DISK_FILE)"
+
   case "${DISK_FMT,,}" in
     raw)
-      if [[ "${ALLOCATE}" == [Nn]* ]]; then
+      if [[ "$ALLOCATE" == [Nn]* ]]; then
 
         # Create an empty file
-        if ! truncate -s "${DISK_SPACE}" "${DISK_FILE}"; then
-          rm -f "${DISK_FILE}"
-          error "Could not create a ${DISK_SPACE} ${DISK_FMT} file for ${DISK_DESC} (${DISK_FILE})" && exit 87
+        if ! truncate -s "$DISK_SPACE" "$DISK_FILE"; then
+          rm -f "$DISK_FILE"
+          error "$FAIL" && exit 87
         fi
 
       else
 
         # Check free diskspace
-        SPACE=$(df --output=avail -B 1 "${DIR}" | tail -n 1)
+        SPACE=$(df --output=avail -B 1 "$DIR" | tail -n 1)
         SPACE_GB=$(( (SPACE + 1073741823)/1073741824 ))
 
         if (( DATA_SIZE > SPACE )); then
-          error "Not enough free space to create a ${DISK_DESC} of ${DISK_SPACE} in ${DIR}, it has only ${SPACE_GB} GB available.."
+          error "Not enough free space to create a $DISK_DESC of $DISK_SPACE in $DIR, it has only $SPACE_GB GB available.."
           error "Please specify a smaller ${DISK_DESC^^}_SIZE or disable preallocation by setting DISK_FMT to \"qcow2\"." && exit 86
         fi
 
         # Create an empty file
-        if ! fallocate -l "${DISK_SPACE}" "${DISK_FILE}"; then
-          if ! truncate -s "${DISK_SPACE}" "${DISK_FILE}"; then
-            rm -f "${DISK_FILE}"
-            error "Could not create a ${DISK_SPACE} ${DISK_FMT} file for ${DISK_DESC} (${DISK_FILE})" && exit 87
+        if ! fallocate -l "$DISK_SPACE" "$DISK_FILE"; then
+          if ! truncate -s "$DISK_SPACE" "$DISK_FILE"; then
+            rm -f "$DISK_FILE"
+            error "$FAIL" && exit 87
           fi
         fi
 
       fi
       ;;
     qcow2)
-      if ! qemu-img create -f "$DISK_FMT" -- "${DISK_FILE}" "${DISK_SPACE}" ; then
-        error "Could not create a ${DISK_SPACE} ${DISK_FMT} file for ${DISK_DESC} (${DISK_FILE})" && exit 89
+      if ! qemu-img create -f "$DISK_FMT" -- "$DISK_FILE" "$DISK_SPACE" ; then
+        rm -f "$DISK_FILE"
+        error "$FAIL" && exit 89
       fi
       ;;
   esac
@@ -209,12 +216,15 @@ addDisk () {
   local DISK_ADDRESS=$7
   local DISK_FMT=$8
 
-  DISK_FILE="${DISK_BASE}.${DISK_EXT}"
+  DISK_FILE="$DISK_BASE.$DISK_EXT"
+  DIR=$(dirname "$DISK_FILE")
+  [ ! -d "$DIR" ] && return 0
 
-  DIR=$(dirname "${DISK_FILE}")
-  [ ! -d "${DIR}" ] && return 0
+  [ -z "$DISK_SPACE" ] && DISK_SPACE="16G"
+  DISK_SPACE=$(echo "$DISK_SPACE" | sed 's/MB/M/g;s/GB/G/g;s/TB/T/g')
+  DATA_SIZE=$(numfmt --from=iec "$DISK_SPACE")
 
-  if ! [ -f "${DISK_FILE}" ] ; then
+  if ! [ -f "$DISK_FILE" ] ; then
     local PREV_EXT
     local PREV_FMT
     local PREV_FILE
@@ -224,51 +234,54 @@ addDisk () {
     else
       PREV_FMT="qcow2"
     fi
-    PREV_EXT="$(fmt2ext "${PREV_FMT}")"
-    PREV_FILE="${DISK_BASE}.${PREV_EXT}"
+    PREV_EXT="$(fmt2ext "$PREV_FMT")"
+    PREV_FILE="$DISK_BASE.$PREV_EXT"
 
-    if [ -f "${PREV_FILE}" ] ; then
-      info "Disk format change detected for ${DISK_DESC} (${PREV_FMT} to ${DISK_FMT}), converting ${PREV_FILE} ..."
-      
-      if ! convertDisk "${PREV_FILE}" "${PREV_FMT}" "${DISK_FILE}" "${DISK_FMT}" ; then
-        info "Disk conversion failed, creating new disk image as fallback."
-        rm -f "${DISK_FILE}"
-      else
-        info "Disk conversion completed succesfully, removing ${PREV_FILE} ..."
-        rm -f "${PREV_FILE}"
+    if [ -f "$PREV_FILE" ] ; then
+
+      info "Detected that ${DISK_DESC^^}_FMT changed from \"$PREV_FMT\" to \"$DISK_FMT\"."
+      info "Starting conversion of $DISK_DESC to this new format, please wait until completed..."
+
+      local TMP_FILE
+      TMP_FILE="$DISK_BASE.tmp"
+      rm -f "$TMP_FILE"
+
+      if ! convertDisk "$PREV_FILE" "$PREV_FMT" "$TMP_FILE" "$DISK_FMT" ; then
+        rm -f "$TMP_FILE"
+        error "Failed to convert $DISK_DESC to $DISK_FMT format." && exit 89
       fi
+
+      mv "$TMP_FILE" "$DISK_FILE"
+      rm -f "$PREV_FILE"
+      info "Conversion of $DISK_DESC completed succesfully!"
     fi
   fi
 
-  [ -z "$DISK_SPACE" ] && DISK_SPACE="16G"
-  DISK_SPACE=$(echo "${DISK_SPACE}" | sed 's/MB/M/g;s/GB/G/g;s/TB/T/g')
-  DATA_SIZE=$(numfmt --from=iec "${DISK_SPACE}")
+  if [ -f "$DISK_FILE" ]; then
 
-  if [ -f "${DISK_FILE}" ]; then
-
-    CUR_SIZE=$(getSize "${DISK_FILE}")
+    CUR_SIZE=$(getSize "$DISK_FILE")
 
     if [ "$DATA_SIZE" -gt "$CUR_SIZE" ]; then
-      resizeDisk "${DISK_FILE}" "${CUR_SIZE}" "${DATA_SIZE}" "${DISK_SPACE}" "${DISK_DESC}" "${DISK_FMT}" || exit $?
+      resizeDisk "$DISK_FILE" "$CUR_SIZE" "$DATA_SIZE" "$DISK_SPACE" "$DISK_DESC" "$DISK_FMT" || exit $?
     fi
 
   else
 
-    createDisk "${DISK_FILE}" "${DISK_SPACE}" "${DISK_DESC}" "${DISK_FMT}" || exit $?
+    createDisk "$DISK_FILE" "$DISK_SPACE" "$DISK_DESC" "$DISK_FMT" || exit $?
 
   fi
 
-  DISK_OPTS="${DISK_OPTS} \
-    -device virtio-scsi-pci,id=hw-${DISK_ID},bus=pcie.0,addr=${DISK_ADDRESS} \
-    -drive file=${DISK_FILE},if=none,id=drive-${DISK_ID},format=${DISK_FMT},cache=${DISK_CACHE},aio=${DISK_IO},discard=${DISK_DISCARD},detect-zeroes=on \
-    -device scsi-hd,bus=hw-${DISK_ID}.0,channel=0,scsi-id=0,lun=0,drive=drive-${DISK_ID},id=${DISK_ID},rotation_rate=${DISK_ROTATION},bootindex=${DISK_INDEX}"
+  DISK_OPTS="$DISK_OPTS \
+    -device virtio-scsi-pci,id=hw-$DISK_ID,bus=pcie.0,addr=$DISK_ADDRESS \
+    -drive file=$DISK_FILE,if=none,id=drive-$DISK_ID,format=$DISK_FMT,cache=$DISK_CACHE,aio=$DISK_IO,discard=$DISK_DISCARD,detect-zeroes=on \
+    -device scsi-hd,bus=hw-$DISK_ID.0,channel=0,scsi-id=0,lun=0,drive=drive-$DISK_ID,id=$DISK_ID,rotation_rate=$DISK_ROTATION,bootindex=$DISK_INDEX"
 
   return 0
 }
 
-DISK_EXT="$(fmt2ext "${DISK_FMT}")" || exit $?
+DISK_EXT="$(fmt2ext "$DISK_FMT")" || exit $?
 
-DISK1_FILE="${STORAGE}/data"
+DISK1_FILE="$STORAGE/data"
 DISK2_FILE="/storage2/data2"
 DISK3_FILE="/storage3/data3"
 DISK4_FILE="/storage4/data4"
@@ -281,12 +294,12 @@ DISK6_FILE="/storage6/data6"
 : ${DISK5_SIZE:=''}
 : ${DISK6_SIZE:=''}
 
-addDisk "userdata"  "${DISK1_FILE}" "${DISK_EXT}" "disk"  "${DISK_SIZE}"  "1" "0xa" "${DISK_FMT}"
-addDisk "userdata2" "${DISK2_FILE}" "${DISK_EXT}" "disk2" "${DISK2_SIZE}" "2" "0xb" "${DISK_FMT}"
-addDisk "userdata3" "${DISK3_FILE}" "${DISK_EXT}" "disk3" "${DISK3_SIZE}" "3" "0xc" "${DISK_FMT}"
-addDisk "userdata4" "${DISK4_FILE}" "${DISK_EXT}" "disk4" "${DISK4_SIZE}" "4" "0xd" "${DISK_FMT}"
-addDisk "userdata5" "${DISK5_FILE}" "${DISK_EXT}" "disk5" "${DISK5_SIZE}" "5" "0xe" "${DISK_FMT}"
-addDisk "userdata6" "${DISK6_FILE}" "${DISK_EXT}" "disk6" "${DISK6_SIZE}" "6" "0xf" "${DISK_FMT}"
+addDisk "userdata" "$DISK1_FILE" "$DISK_EXT" "disk"  "$DISK_SIZE"  "1" "0xa" "$DISK_FMT" || exit $?
+addDisk "userdata2" "$DISK2_FILE" "$DISK_EXT" "disk2" "$DISK2_SIZE" "2" "0xb" "$DISK_FMT" || exit $?
+addDisk "userdata3" "$DISK3_FILE" "$DISK_EXT" "disk3" "$DISK3_SIZE" "3" "0xc" "$DISK_FMT" || exit $?
+addDisk "userdata4" "$DISK4_FILE" "$DISK_EXT" "disk4" "$DISK4_SIZE" "4" "0xd" "$DISK_FMT" || exit $?
+addDisk "userdata5" "$DISK5_FILE" "$DISK_EXT" "disk5" "$DISK5_SIZE" "5" "0xe" "$DISK_FMT" || exit $?
+addDisk "userdata6" "$DISK6_FILE" "$DISK_EXT" "disk6" "$DISK6_SIZE" "6" "0xf" "$DISK_FMT" || exit $?
 
 addDevice () {
 
@@ -295,13 +308,13 @@ addDevice () {
   local DISK_INDEX=$3
   local DISK_ADDRESS=$4
 
-  [ -z "${DISK_DEV}" ] && return 0
-  [ ! -b "${DISK_DEV}" ] && error "Device ${DISK_DEV} cannot be found! Please add it to the 'devices' section of your compose file." && exit 55
+  [ -z "$DISK_DEV" ] && return 0
+  [ ! -b "$DISK_DEV" ] && error "Device $DISK_DEV cannot be found! Please add it to the 'devices' section of your compose file." && exit 55
 
-  DISK_OPTS="${DISK_OPTS} \
-    -device virtio-scsi-pci,id=hw-${DISK_ID},bus=pcie.0,addr=${DISK_ADDRESS} \
-    -drive file=${DISK_DEV},if=none,id=drive-${DISK_ID},format=raw,cache=${DISK_CACHE},aio=${DISK_IO},discard=${DISK_DISCARD},detect-zeroes=on \
-    -device scsi-hd,bus=hw-${DISK_ID}.0,channel=0,scsi-id=0,lun=0,drive=drive-${DISK_ID},id=${DISK_ID},rotation_rate=${DISK_ROTATION},bootindex=${DISK_INDEX}"
+  DISK_OPTS="$DISK_OPTS \
+    -device virtio-scsi-pci,id=hw-$DISK_ID,bus=pcie.0,addr=$DISK_ADDRESS \
+    -drive file=$DISK_DEV,if=none,id=drive-$DISK_ID,format=raw,cache=$DISK_CACHE,aio=$DISK_IO,discard=$DISK_DISCARD,detect-zeroes=on \
+    -device scsi-hd,bus=hw-$DISK_ID.0,channel=0,scsi-id=0,lun=0,drive=drive-$DISK_ID,id=$DISK_ID,rotation_rate=$DISK_ROTATION,bootindex=$DISK_INDEX"
 
   return 0
 }
@@ -313,11 +326,11 @@ addDevice () {
 : ${DEVICE5:=''}
 : ${DEVICE6:=''}
 
-addDevice "userdata7" "${DEVICE}" "7" "0x6"
-addDevice "userdata8" "${DEVICE2}" "8" "0x7"
-addDevice "userdata9" "${DEVICE3}" "9" "0x8"
-addDevice "userdata4" "${DEVICE4}" "4" "0xd"
-addDevice "userdata5" "${DEVICE5}" "5" "0xe"
-addDevice "userdata6" "${DEVICE6}" "6" "0xf"
+addDevice "userdata7" "$DEVICE" "7" "0x6" || exit $?
+addDevice "userdata8" "$DEVICE2" "8" "0x7" || exit $?
+addDevice "userdata9" "$DEVICE3" "9" "0x8" || exit $?
+addDevice "userdata4" "$DEVICE4" "4" "0xd" || exit $?
+addDevice "userdata5" "$DEVICE5" "5" "0xe" || exit $?
+addDevice "userdata6" "$DEVICE6" "6" "0xf" || exit $?
 
 return 0