Public bug reported:
I performed a backup to tape of three ZFS filesystem snapshots with this
command:
tar -cPvzf /dev/st0 /tambor/luki/.zfs/snapshot/backup/
/tambor/caligrafix/.zfs/snapshot/backup/ /tambor/pub/.zfs/snapshot/backup/
Then when verifying the backup with this command:
tar -dPvzf /dev/st0 /tambor/luki/.zfs/snapshot/backup/
/tambor/caligrafix/.zfs/snapshot/backup/ /tambor/pub/.zfs/snapshot/backup/
I got errors such as:
/tambor/pub/.zfs/snapshot/backup/gallery.img: Not linked to
/tambor/pub/.zfs/snapshot/backup/gallery.img
Listing the archive content for this entry shows that tar thought there was a
hard link:
hrw------- libvirt-qemu/kvm 0 2016-06-30 16:42
/tambor/pub/.zfs/snapshot/backup/gallery.img link to
tambor/luki/.zfs/snapshot/backup/vms/luki-odoo.qcow2
On the actual filesystem, stat shows the following about these files:
gpothier@lerne:~$ stat /tambor/pub/.zfs/snapshot/backup/gallery.img
File: '/tambor/pub/.zfs/snapshot/backup/gallery.img'
Size: 21474836480 Blocks: 38391905 IO Block: 131072 regular file
Device: 28h/40d Inode: 9 Links: 1
Access: (0600/-rw-------) Uid: ( 106/libvirt-qemu) Gid: ( 106/ kvm)
Access: 2016-06-14 08:17:12.243476594 -0400
Modify: 2016-06-30 16:42:05.151696559 -0400
Change: 2016-06-30 16:42:05.151696559 -0400
Birth: -
gpothier@lerne:~$ stat /tambor/luki/.zfs/snapshot/backup/vms/luki-odoo.qcow2
File: '/tambor/luki/.zfs/snapshot/backup/vms/luki-odoo.qcow2'
Size: 152349835264 Blocks: 39049233 IO Block: 131072 regular file
Device: 29h/41d Inode: 9 Links: 1
Access: (0600/-rw-------) Uid: ( 106/libvirt-qemu) Gid: ( 106/ kvm)
Access: 2016-06-14 08:17:12.711478957 -0400
Modify: 2016-06-30 16:42:08.691712436 -0400
Change: 2016-06-30 16:42:08.691712436 -0400
Birth: -
They have the same inode number, but a different device number. And their link
count is 1.
So the heuristics tar uses to determine if a file is a hard link are not
correct. In this case this is a big deal, as it produced an incomplete backup.
I will have to use the --hard-dereference flag to work around it.
ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: tar 1.27.1-1
ProcVersionSignature: Ubuntu 3.13.0-88.135-generic 3.13.11-ckt39
Uname: Linux 3.13.0-88-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
Date: Sat Jul 2 10:43:43 2016
InstallationDate: Installed on 2014-05-29 (764 days ago)
InstallationMedia: Ubuntu-Server 14.04 LTS "Trusty Tahr" - Release amd64
(20140416.2)
SourcePackage: tar
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: tar (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug trusty
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https://bugs.launchpad.net/bugs/1598443
Title:
tar mistakenly thinks two distinct files on a zfs volume are hard
linked
Status in tar package in Ubuntu:
New
Bug description:
I performed a backup to tape of three ZFS filesystem snapshots with this
command:
tar -cPvzf /dev/st0 /tambor/luki/.zfs/snapshot/backup/
/tambor/caligrafix/.zfs/snapshot/backup/ /tambor/pub/.zfs/snapshot/backup/
Then when verifying the backup with this command:
tar -dPvzf /dev/st0 /tambor/luki/.zfs/snapshot/backup/
/tambor/caligrafix/.zfs/snapshot/backup/ /tambor/pub/.zfs/snapshot/backup/
I got errors such as:
/tambor/pub/.zfs/snapshot/backup/gallery.img: Not linked to
/tambor/pub/.zfs/snapshot/backup/gallery.img
Listing the archive content for this entry shows that tar thought there was a
hard link:
hrw------- libvirt-qemu/kvm 0 2016-06-30 16:42
/tambor/pub/.zfs/snapshot/backup/gallery.img link to
tambor/luki/.zfs/snapshot/backup/vms/luki-odoo.qcow2
On the actual filesystem, stat shows the following about these files:
gpothier@lerne:~$ stat /tambor/pub/.zfs/snapshot/backup/gallery.img
File: '/tambor/pub/.zfs/snapshot/backup/gallery.img'
Size: 21474836480 Blocks: 38391905 IO Block: 131072 regular file
Device: 28h/40d Inode: 9 Links: 1
Access: (0600/-rw-------) Uid: ( 106/libvirt-qemu) Gid: ( 106/ kvm)
Access: 2016-06-14 08:17:12.243476594 -0400
Modify: 2016-06-30 16:42:05.151696559 -0400
Change: 2016-06-30 16:42:05.151696559 -0400
Birth: -
gpothier@lerne:~$ stat /tambor/luki/.zfs/snapshot/backup/vms/luki-odoo.qcow2
File: '/tambor/luki/.zfs/snapshot/backup/vms/luki-odoo.qcow2'
Size: 152349835264 Blocks: 39049233 IO Block: 131072 regular file
Device: 29h/41d Inode: 9 Links: 1
Access: (0600/-rw-------) Uid: ( 106/libvirt-qemu) Gid: ( 106/ kvm)
Access: 2016-06-14 08:17:12.711478957 -0400
Modify: 2016-06-30 16:42:08.691712436 -0400
Change: 2016-06-30 16:42:08.691712436 -0400
Birth: -
They have the same inode number, but a different device number. And their
link count is 1.
So the heuristics tar uses to determine if a file is a hard link are not
correct. In this case this is a big deal, as it produced an incomplete backup.
I will have to use the --hard-dereference flag to work around it.
ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: tar 1.27.1-1
ProcVersionSignature: Ubuntu 3.13.0-88.135-generic 3.13.11-ckt39
Uname: Linux 3.13.0-88-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
Date: Sat Jul 2 10:43:43 2016
InstallationDate: Installed on 2014-05-29 (764 days ago)
InstallationMedia: Ubuntu-Server 14.04 LTS "Trusty Tahr" - Release amd64
(20140416.2)
SourcePackage: tar
UpgradeStatus: No upgrade log present (probably fresh install)
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