2017-12-14 Playing with BTRFS quota limits - Grzegorz Wierzowiecki

2017-12-14-btrfs-try-to-btrfs-quota-qgroup.sh

#!/bin/bash
# 2017-12-14 Playing with BTRFS quota limits - Grzegorz Wierzowiecki
# gist: 
# Below script is prepared for easy experimentation, and should run copy-and-paste
# (you need permissions to create lvm groups, etc. therefore root)
# It
# * setup 128MiB btrfstest in selected volume group
# * setup quotas (32MiB and 64MiB) and test them
# * cleanup
# Helpful references:
# https://wiki.archlinux.org/index.php/Btrfs
# https://btrfs.wiki.kernel.org/index.php/Quota_support
# https://serverfault.com/a/803702/65137
# https://gist.github.com/mazgi/d7317aa1959ca4434ab1
# https://btrfs.wiki.kernel.org/index.php/UseCases#How_do_we_implement_quota_in_BTRFS.3F

# input parameters
read -p 'Provide your LVM volume group:' vgname

# rest of script should be fully automatic ready for copy&paste
lvname=btrfstest
# create 128m lvm volume for this test
lvcreate -L 128m -n "${lvname?}" "${vgname?}"
lvpath=/dev/mapper/"${vgname?}-${lvname?}"
# make it btrfs
mkfs.btrfs -L "${lvname?}" "${lvpath?}"
# mount it
mntpath="$(mktemp -d --suffix="_$lvname")"
mount -t btrfs "${lvpath?}" "${mntpath?}"
# check it's size
df -h "$mntpath"
# create subvolumes subA and subB
btrfs subvolume create "${mntpath?}"/subA
btrfs subvolume create "${mntpath?}"/subB
# list subvolumes
btrfs subvolume list "${mntpath?}"
# example output:
# > ID 256 gen 8 top level 5 path subA
# > ID 257 gen 9 top level 5 path subB
#
# Try to enable quotas
btrfs quota enable "${mntpath?}"
btrfs quota rescan "${mntpath?}"
# Now execute:
btrfs subvolume list "${mntpath?}" | cut -d' ' -f2 | xargs -I{} -n1 btrfs qgroup create 0/{} "${mntpath?}"
# effectively executing in case of above IDs:
# btrfs qgroup create 0/256 "${mntpath?}"
# btrfs qgroup create 0/257 "${mntpath?}"
btrfs qgroup show "${mntpath?}"
# in our case may output:
# > qgroupid         rfer         excl 
# > --------         ----         ---- 
# > 0/5          16.00KiB     16.00KiB 
# > 0/256           0.00B        0.00B 
# > 0/257           0.00B        0.00B
#
# So, let's run rescan, wait a bit and try show again, more detailed
btrfs quota rescan "${mntpath?}"
btrfs qgroup show -perc "${mntpath?}"
# no it outputs:
# > qgroupid         rfer         excl     max_rfer     max_excl parent  child 
# > --------         ----         ----     --------     -------- ------  ----- 
# > 0/5          16.00KiB     16.00KiB         none         none ---     ---  
# > 0/256        16.00KiB     16.00KiB         none         none ---     ---  
# > 0/257        16.00KiB     16.00KiB         none         none ---     ---  
#
# Let's apply limits:
# (according to https://btrfs.wiki.kernel.org/index.php/UseCases#How_do_we_implement_quota_in_BTRFS.3F )
btrfs qgroup limit 32M "${mntpath?}"/subA
btrfs qgroup limit 64M "${mntpath?}"/subB

btrfs qgroup show -perc "${mntpath?}"
# in our case:
# > qgroupid         rfer         excl     max_rfer     max_excl parent  child 
# > --------         ----         ----     --------     -------- ------  ----- 
# > 0/5          16.00KiB     16.00KiB         none         none ---     ---  
# > 0/256        16.00KiB     16.00KiB     32.00MiB         none ---     ---  
# > 0/257        16.00KiB     16.00KiB     64.00MiB         none ---     ---  
btrfs qgroup show -reF "${mntpath?}"
# output:
# > qgroupid         rfer         excl     max_rfer     max_excl 
# > --------         ----         ----     --------     -------- 
# > 0/5          16.00KiB     16.00KiB         none         none
btrfs qgroup show -reF "${mntpath?}"/subA
# > qgroupid         rfer         excl     max_rfer     max_excl 
# > --------         ----         ----     --------     -------- 
# > 0/256        16.00KiB     16.00KiB     32.00MiB         none 
btrfs qgroup show -reF "${mntpath?}"/subB
# > qgroupid         rfer         excl     max_rfer     max_excl 
# > --------         ----         ----     --------     -------- 
# > 0/257        16.00KiB     16.00KiB     64.00MiB         none 

# Let's test it!
cat /dev/urandom > "${mntpath?}"/subA/file_with_urand
cat /dev/urandom > "${mntpath?}"/subB/file_with_urand
ls -lha "${mntpath?}"/sub{A,B}/file_with_urand
# > -rw-r--r-- 1 root root 32M Dec 15 19:51 /tmp/tmp.2AMRQgSfdP_btrfstest/subA/file_with_urand
# > -rw-r--r-- 1 root root 64M Dec 15 19:51 /tmp/tmp.2AMRQgSfdP_btrfstest/subB/file_with_urand

# Cleanup after tests:
umount "${mntpath?}"
rmdir "${mntpath?}"
lvremove -y "${lvpath?}"