Bug 816098

Summary:	virt-make-fs fails to make a btrfs filesystem because it doesn't allocate enough space
Product:	[Community] Virtualization Tools	Reporter:	Richard W.M. Jones <rjones>
Component:	libguestfs	Assignee:	Richard W.M. Jones <rjones>
Status:	CLOSED UPSTREAM	QA Contact:
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	unspecified	CC:	dyasny, mbooth, virt-maint
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Fixed In Version:		Doc Type:	Bug Fix
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Last Closed:	2012-05-03 15:49:08 UTC	Type:	Bug
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
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Description Richard W.M. Jones 2012-04-25 09:19:58 UTC

Description of problem:

btrfs has a minimum filesystem size of 256 MB.  virt-make-fs
doesn't take this into account when estimating the size of
filesystem to create, so if the input files are less than this
size it will fail with an error similar to:

mkfs: btrfs: /dev/vda1: device /dev/vda1 is too small (must be at least 256 MB) at /usr/bin/virt-make-fs line 451.

Version-Release number of selected component (if applicable):

1.17.33

How reproducible:

100%

Steps to Reproduce:
1. Choose a small tarball (much smaller than 256 MB in size)
2. virt-make-fs -F qcow2 -t btrfs --partition=mbr input.tar output.qcow2

Actual results:

Fails with an error as above.

Expected results:

It should increase the estimate to the minimum size and thus
not fail.

Additional info:

Comment 1 Richard W.M. Jones 2012-04-25 09:25:29 UTC

Note that the overhead of btrfs is much larger than expected.
eg: With a 6 MB tarball, a 512 MB disk doesn't have enough space:

$ virt-make-fs -F qcow2 -t btrfs --partition=mbr --size=512M \
    libguestfs-1.17.1.tar.gz /tmp/disk.qcow2
Formatting '/tmp/disk.qcow2', fmt=qcow2 size=536870912 encryption=off cluster_size=65536 
virt-make-fs: error copying contents into filesystem
An error here usually means that the program did not estimate the
filesystem size correctly.  Please read the BUGS section of the manpage.
tar_in: tar subcommand failed on directory: /: tar: libguestfs-1.17.1/ChangeLog: Cannot write: No space left on device
tar: libguestfs-1.17.1/.gitignore: Cannot write: No space left on device
[...]

With a 1 GB filesystem, only 388 MB is usable, indicating an
overhead of 636 MB just for btrfs(!)

$ virt-make-fs ... --size=1G ...
$ virt-df -h /tmp/disk.qcow2 
Filesystem                                Size       Used  Available  Use%
disk.qcow2:/dev/sda1                      1.0G        37M       351M    4%

Comment 2 Richard W.M. Jones 2012-04-25 09:28:45 UTC

See also:
https://btrfs.wiki.kernel.org/articles/f/a/q/FAQ_1fe9.html#Why_does_df_show_incorrect_free_space_for_my_RAID_volume.3F

Comment 3 Richard W.M. Jones 2012-05-03 12:39:28 UTC

Link should be:

https://btrfs.wiki.kernel.org/index.php/FAQ#Why_are_there_so_many_ways_to_check_the_amount_of_free_space.3F

Comment 4 Richard W.M. Jones 2012-05-03 13:37:03 UTC

Patches posted to the upstream mailing list:
https://www.redhat.com/archives/libguestfs/2012-May/msg00015.html

Comment 5 Richard W.M. Jones 2012-05-03 15:49:08 UTC

Fixed in 1.17.39.