Btrfs
I tried to have a root filesystem into btrfs for a Gandi server, and succeed after a number of trial-error. Here are my steps if it can be useful to others.
WARNING: this is EXPERIMENTAL and could cause DATA LOSS.
This was updated on 2020-09-24 for Debian 10 buster + GandiV5 and works probably also for Debian 11 bullseye. An older version was for Debian 9 jessie or Ubuntu 18.04 LTS + GandiV4.
Sommaire
Create the server
On GandiV5, create a new server with e.g. 1 proc, 256 Mio RAM, 1 system disk, Debian 10 buster.
Update the packages:
apt update && apt upgrade -y
Define backports for Debian 10 (btrfs-progs must contain btrfs-convert, see this Debian bug) (this is not needed for Debian 11):
echo 'deb https://deb.debian.org/debian buster-backports main' > /etc/apt/sources.list.d/debian-backports.list
Install btrfs-progs:
apt update && apt install -t buster-backports btrfs-progs
On GandiV5, stop the server, open the page about the system disk, clone the system disk with another (definitive) name, and attach this cloned disk to the server, start the server.
Convert to btrfs
- Mostly from [1]
Display the active root filesystem, and you will be able to deduce what is the cloned filesystem:
ls /dev/xvd* mount|grep xvd blkid
Let’s say /dev/xvdb1 is the clone filesystem, we convert it to btrfs: (man 8 btrfs-convert)
fsck.ext4 -f /dev/xvdb1 # optional btrfs-convert -p /dev/xvdb1
Here, I obtained the following error:
root@test:~# btrfs-convert -p /dev/xvdb1 create btrfs filesystem: blocksize: 4096 nodesize: 16384 features: extref, skinny-metadata (default) creating ext2 image file creating btrfs metadata Unable to find block group for 0 27081] Unable to find block group for 0 Unable to find block group for 0 ctree.c:2245: split_leaf: BUG_ON `1` triggered, value 1 btrfs-convert(+0x11b5a)[0x559c159c1b5a] btrfs-convert(+0x1589b)[0x559c159c589b] btrfs-convert(btrfs_search_slot+0x269)[0x559c159c6401] btrfs-convert(btrfs_insert_empty_items+0x92)[0x559c159c7b3c] btrfs-convert(btrfs_record_file_extent+0x1bc)[0x559c159d46b4] btrfs-convert(record_file_blocks+0x14a)[0x559c159bfe92] btrfs-convert(+0x10349)[0x559c159c0349] btrfs-convert(+0x1135f)[0x559c159c135f] btrfs-convert(main+0x1f59)[0x559c159bdefb] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7f4c11c3bb97] btrfs-convert(_start+0x2a)[0x559c159bb5ca] Aborted
According to [2] and [3], it can be worked around: (this command could take some hours, depending on disk size and number of files)
btrfs-convert -d -p /dev/xvdb1
or even:
btrfs-convert -n -d -p /dev/xvdb1
Or, if still unsuccessful, try to add free space, or if still unsuccessfull, re-compile btrfs-progs in version 4.17.1 (this last try worked for me for 50 Gio disk with 24 Gio free space on Debian 9 jessie, expanded after its original size was 30 Gio (=4 Gio free space)).
Then, mount the filesystem and delete the old ext4 snapshot:
mount /dev/xvdb1 /mnt btrfs subvolume delete /mnt/ext2_saved btrfs filesystem defrag -r /mnt # could take dozen of minuts btrfs balance start /mnt # could take hours
Promote as root filesystem
- Mostly from [4]
Enter the chrooted system:
for i in dev dev/pts proc sys; do mount --bind /$i /mnt/$i; done chroot /mnt blkid|grep xvdb1 vi /etc/fstab
Edit the root filesystem with: (the UUID is from the command blkid)
UUID=a74f5787-aee1-4981-b7e6-fbd3cb6ac919 / btrfs defaults 0 1
(in vi, type "dd" to remove a line, "i" to enter in edit mode, Esc to quit edit mode, ":x" to save and quit.)
Update grub:
update-grub
Change the reference of the root device (will be xvda1 when it will be the root device):
sed -i s/xvdb1/xvda1/g /boot/grub/grub.cfg
Quit:
exit for i in dev/pts dev proc sys; do umount /mnt/$i; done umount /mnt exit
Define the cooked disk as boot disk
In Gandi V5 interface, stop the server, detach the old root disk and define the cooked disk as "Use to start".
Launch the server (it should correctly start, even if the /boot directory is on the main partition / (some old documents said it didn’t work because grub didn’t know the btrfs filesystem, but it is fixed now)).
df -hT
It should show something like:
/dev/xvda1 btrfs 50G 32G 19G 63% /
Delete the old root disk.
You can delete the packages grub-efi-amd64 and grub-efi-amd64-bin since they are not used, but keep /etc/default/grub with Gandi customisations:
cp -a /etc/default/grub /root/grub apt-get purge -y grub-efi-amd64 grub-efi-amd64-bin mv /root/grub /etc/default/grub update-grub # to check it still work and you should reboot now to be sure it reboots correctly
External links
Debug data:
-
Start request GET /Btrfs?oldid=658080
HTTP HEADERS:
CONNECTION: Keep-Alive
HOST: wiki.seb35.fr
ACCEPT-ENCODING: br,gzip
IF-MODIFIED-SINCE: Sun, 25 Oct 2020 14:22:22 GMT
ACCEPT-LANGUAGE: en-US,en;q=0.5
ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
USER-AGENT: CCBot/2.0 (https://commoncrawl.org/faq/)
CONTENT-LENGTH:
CONTENT-TYPE: -
[caches] main: EmptyBagOStuff, message: SqlBagOStuff, parser: SqlBagOStuff
-
[caches] LocalisationCache: using store LCStoreCDB
-
Fully initialised
-
Connected to database 0 at localhost:/run/mysqld/mysqld.sock
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Title::getRestrictionTypes: applicable restrictions to [[Btrfs]] are {edit,move}
-
[ContentHandler] Created handler for wikitext: WikitextContentHandler
-
Connected to database 0 at localhost:/run/mysqld/mysqld.sock
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[DBPerformance] [GET] Expectation (masterConns <= 0) by MediaWiki::main not met:
[connect to localhost:/run/mysqld/mysqld.sock (wiki_seb35)]
TransactionProfiler.php line 271 calls wfBacktrace()
TransactionProfiler.php line 128 calls TransactionProfiler->reportExpectationViolated()
LoadBalancer.php line 517 calls TransactionProfiler->recordConnection()
SqlBagOStuff.php line 160 calls LoadBalancer->getConnection()
SqlBagOStuff.php line 245 calls SqlBagOStuff->getDB()
SqlBagOStuff.php line 219 calls SqlBagOStuff->getMulti()
MessageCache.php line 300 calls SqlBagOStuff->get()
MessageCache.php line 881 calls MessageCache->load()
MessageCache.php line 800 calls MessageCache->getMsgFromNamespace()
MessageCache.php line 737 calls MessageCache->getMessageFromFallbackChain()
Message.php line 1075 calls MessageCache->get()
Message.php line 698 calls Message->fetchMessage()
Message.php line 789 calls Message->toString()
OutputPage.php line 930 calls Message->text()
OutputPage.php line 977 calls OutputPage->setHTMLTitle()
Article.php line 512 calls OutputPage->setPageTitle()
ViewAction.php line 44 calls Article->view()
MediaWiki.php line 463 calls ViewAction->show()
MediaWiki.php line 269 calls MediaWiki->performAction()
MediaWiki.php line 634 calls MediaWiki->performRequest()
MediaWiki.php line 482 calls MediaWiki->main()
index.php line 41 calls MediaWiki->run()
index.php line 31 calls require() -
IP: 18.215.185.97
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[MessageCache] MessageCache::load: Loading fr... got from global cache
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Unstubbing $wgParser on call of $wgParser::firstCallInit from MessageCache::transform
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Parser: using preprocessor: Preprocessor_DOM
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Unstubbing $wgLang on call of $wgLang::_unstub from ParserOptions::__construct
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Article::view using parser cache: yes
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Parser cache options found.
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ParserOutput cache found.
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Article::view: showing parser cache contents for current rev permalink
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[username] User::isValidUserName: '18.215.185.97' invalid due to empty, IP, slash, length, or lowercase
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[MessageCache] MessageCache::load: Loading en... got from global cache
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Title::getRestrictionTypes: applicable restrictions to [[Btrfs]] are {edit,move}