Script to rebalance the large zfs dataset minimizing the downtime

rebalance.sh

#!/usr/local/bin/zsh

set -e

## -- configuration -- ##

# Specify the dataset name that needs to be rebalanced and provide stop_services and
# start_services functions

dataset="pool1/storagenode-one"

jail="storj"

stop_services()
{
  iocage stop "$jail"
}

start_services()
{
  iocage start "$jail"
}

## -- implementation -- ##

# total umber of passes
np=6

# Name of the temporary dataset
target="${dataset}-temp"

# Name(s) of the temporary snapshots(s)
snapshot="tmpcloning"

## -- helpers -- ##

send_snapshot()
{
  if [ "1" -eq "$1" ]; then
    echo "Copying initial snapshot $1"
	zfs snapshot -r "${dataset}@$snapshot$1"
	zfs send -Rv "${dataset}@$snapshot$1" | zfs receive "$target"
  else
    echo "Copying incremental snapsgot $1 since $(($1-1))"
    zfs snapshot -r "${dataset}@$snapshot$1"
    zfs send -Rvi "${dataset}@$snapshot$(($1-1))" "${dataset}@$snapshot$1" | zfs receive "$target"
  fi
}

rename_datasets()
{
  echo "Renaming datasets"
  zfs rename ${dataset} ${dataset}-old
  zfs rename $target ${dataset}
}

destroy_tmp_data()
{
  for i in $(seq $np); do
    zfs destroy -r "${dataset}-old@$snapshot$i"
    zfs destroy -r "${dataset}@$snapshot$i"
  done
  zfs destroy -r "${dataset}-old"
}

## -- action -- ##

for i in $(seq $(("$np"-1))); do
  send_snapshot "$i"
done

stop_services

send_snapshot $np

rename_datasets

start_services

destroy_tmp_data