Let lvm create metadata volume automatically

Right now we create lvm metadata volume first and then data volume and then
pass it to lvm to convert it into a thin pool (lvconvert). This means lvm
internally creates an spare logical volume (used during repair) and needs
free space in volume group for that spare volume. But lvm does not tell
how big an spare volume will be so caller does not know how much free space
to leave in volume group. And that means if user passes in DATA_SIZE=100%FREE
by the time we call lvconvert, there is no free space left and lvconvert
fails. And we leave the system in uncleaned state (metadata and data volumes
behind).

Dusty came up with idea that why not let lvm create metadata, data and spare
volume. That way docker-storage-setup does not have to deal with how much
free space to leave. Also use option --poolmetadatasize option to specify
size of metadata, so that we retain control on how big metadata volume
should be. 

This should allow users to pass in DATA_SIZE as 100%FREE. Though lvm
developers say it is not a good idea to fill up volume group completely
and leave some space free so that later either metadata, data or spare
volume can grow as need be. 

This patch changes behavior of MIN_DATA_SIZE. Previously we will make sure
free space in VG is more than MIN_DATA_SIZE before creating data volume
(and after crating metadata volume). Now we do the same check before
creating metadata volume. Given metadata volume is very small (.1% of data
size). This can be considered sort of round off error and should not
be a real problem.

Reported-by: Dusty Mabe <[email protected]>
Signed-off-by: Vivek Goyal <[email protected]>

docker-storage-setup.sh

@@ -55,8 +55,6 @@ set -e
 # Note: lvm2 version should be same or higher than lvm2-2.02.112 for lvm
 #       thin pool functionality to work properly.
 POOL_LV_NAME="docker-pool"
-DATA_LV_NAME=$POOL_LV_NAME
-META_LV_NAME="${POOL_LV_NAME}meta"
 
 DOCKER_STORAGE="/etc/sysconfig/docker-storage"
 STORAGE_DRIVERS="devicemapper overlay overlay2"
@@ -209,7 +207,7 @@ get_devicemapper_config_options() {
   # docker expects device mapper device and not lvm device. Do the conversion.
   eval $( lvs --nameprefixes --noheadings -o lv_name,kernel_major,kernel_minor $VG | while read line; do
     eval $line
-    if [ "$LVM2_LV_NAME" = "$DATA_LV_NAME" ]; then
+    if [ "$LVM2_LV_NAME" = "$POOL_LV_NAME" ]; then
       echo POOL_DEVICE_PATH=/dev/mapper/$( cat /sys/dev/block/${LVM2_LV_KERNEL_MAJOR}:${LVM2_LV_KERNEL_MINOR}/dm/name )
     fi
   done )
@@ -246,27 +244,6 @@ EOF
   mv -Z $DOCKER_STORAGE.tmp $DOCKER_STORAGE
 }
 
-create_metadata_lv() {
-  # If metadata lvm already exists (failures from previous run), then
-  # don't create it.
-  # TODO: Modify script to cleanup meta and data lvs if failure happened
-  # later. Don't exit with error leaving partially created lvs behind.
-
-  if lvs -a $VG/${META_LV_NAME} --noheadings &>/dev/null; then
-    Info "Metadata volume $META_LV_NAME already exists. Not creating a new one."
-    return 0
-  fi
-
-  # Reserve 0.1% of the free space in the VG for docker metadata.
-  # Calculating the based on actual data size might be better, but is
-  # more difficult do to the range of possible inputs.
-  VG_SIZE=$( vgs --noheadings --nosuffix --units s -o vg_size $VG )
-  META_SIZE=$(( $VG_SIZE / 1000 + 1 ))
-  if [ ! -n "$META_LV_SIZE" ]; then
-    lvcreate -y -L ${META_SIZE}s -n $META_LV_NAME $VG
-  fi
-}
-
 convert_size_in_bytes() {
   local size=$1 prefix suffix
 
@@ -368,9 +345,13 @@ check_min_data_size_condition() {
   fi
 }
 
-create_data_lv() {
+create_lvm_thin_pool () {
+  if [ -z "$DEVS_ABS" ] && [ -z "$VG_EXISTS" ]; then
+    Fatal "Specified volume group $VG does not exist, and no devices were specified"
+  fi
+
   if [ ! -n "$DATA_SIZE" ]; then
-    Fatal "Data volume creation failed. No DATA_SIZE specified"
+    Fatal "DATA_SIZE not specified."
   fi
 
   if ! check_data_size_syntax $DATA_SIZE; then
@@ -379,27 +360,25 @@ create_data_lv() {
 
   check_min_data_size_condition
 
-  # TODO: Error handling when DATA_SIZE > available space.
-  if [[ $DATA_SIZE == *%* ]]; then
-    lvcreate -y -l $DATA_SIZE -n $DATA_LV_NAME $VG
-  else
-    lvcreate -y -L $DATA_SIZE -n $DATA_LV_NAME $VG
-  fi
-}
-
-create_lvm_thin_pool () {
-  if [ -z "$DEVS_ABS" ] && [ -z "$VG_EXISTS" ]; then
-    Fatal "Specified volume group $VG does not exist, and no devices were specified"
+  # Calculate size of metadata lv. Reserve 0.1% of the free space in the VG
+  # for docker metadata.
+  VG_SIZE=$(vgs --noheadings --nosuffix --units s -o vg_size $VG)
+  META_SIZE=$(( $VG_SIZE / 1000 + 1 ))
+  if [ -z "$META_SIZE" ];then
+    Fatal "Failed to calculate size of metadata volume"
   fi
 
-  # First create metadata lv. Down the line let lvm2 create it automatically.
-  create_metadata_lv
-  create_data_lv
-
   if [ -n "$CHUNK_SIZE" ]; then
     CHUNK_SIZE_ARG="-c $CHUNK_SIZE"
   fi
-  lvconvert -y --zero n $CHUNK_SIZE_ARG --thinpool $VG/$DATA_LV_NAME --poolmetadata $VG/$META_LV_NAME
+
+  if [[ $DATA_SIZE == *%* ]]; then
+    DATA_SIZE_ARG="-l $DATA_SIZE"
+  else
+    DATA_SIZE_ARG="-L $DATA_SIZE"
+  fi
+
+  lvcreate -y --thin --zero n $CHUNK_SIZE_ARG --poolmetadatasize ${META_SIZE}s $DATA_SIZE_ARG -n $POOL_LV_NAME $VG
 }
 
 get_configured_thin_pool() {