Hey guys,
We've got a bunch of hosts with multiple spinning disks providing file
server duties with xfs.
Some of the filesystems will go into a state where they report
negative used space - e.g. available is greater than total.
This appears to be purely cosmetic, as we can still write data to (and
read from) the filesystem, but it throws out our reporting data.
We can (temporarily) fix the issue by unmounting and running
`xfs_repair` on the filesystem, but it soon reoccurs.
Does anybody have any ideas as to why this might be happening and how
to prevent it? Can userspace processes affect change to the xfs
superblock?
Example of a 'good' filesystem on the host:
$ sudo df -k /dev/sdac
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdac 9764349952 7926794452 1837555500 82% /srv/node/sdac
$ sudo strace df -k /dev/sdac |& grep statfs
statfs("/srv/node/sdac", {f_type=0x58465342, f_bsize=4096,
f_blocks=2441087488, f_bfree=459388875, f_bavail=459388875,
f_files=976643648, f_ffree=922112135, f_fsid={16832, 0},
f_namelen=255, f_frsize=4096, f_flags=3104}) = 0
$ sudo xfs_db -r /dev/sdac
[ snip ]
icount = 54621696
free = 90183
fdblocks = 459388955
Example of a 'bad' filesystem on the host:
$ sudo df -k /dev/sdad
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdad 9764349952 -9168705440 18933055392 - /srv/node/sdad
$ sudo strace df -k /dev/sdad |& grep statfs
statfs("/srv/node/sdad", {f_type=0x58465342, f_bsize=4096,
f_blocks=2441087488, f_bfree=4733263848, f_bavail=4733263848,
f_files=976643648, f_ffree=922172221, f_fsid={16848, 0},
f_namelen=255, f_frsize=4096, f_flags=3104}) = 0
$ sudo xfs_db -r /dev/sdad
[ snip ]
icount = 54657600
ifree = 186173
fdblocks = 4733263928
Host environment:
$ uname -a
Linux hostname 4.15.0-47-generic #50~16.04.1-Ubuntu SMP Fri Mar 15
16:06:21 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.5 LTS
Release: 16.04
Codename: xenial
Thank you!
Tim
