Bug#651425: lvm2 pvs output cripled so ganeti fails to create guest instances

Jon Bendtsen jbendtsen at laerdal.dk
Thu Dec 8 15:42:01 UTC 2011

Package: lvm2
Version: 2.02.88-2
Severity: normal

Dear Maintainer,
*** Please consider answering these questions, where appropriate ***

   * What led up to the situation?
   * What exactly did you do (or not do) that was effective (or
   * What was the outcome of this action?
   * What outcome did you expect instead?

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Trying out Ganeti 2.4.5 I ran into a problem where ganeti could not create guest instances.
With the help of spadaccio in #ganeti on freenode, I tracked it down to out from pvs not
being as it was supposed to.

pvs --noheadings --nosuffix --units=m --unbuffered '--separator=|' -opv_name,vg_name,pv_free,pv_attr

If i install lvm2_2.02.66-5_amd64.deb from squeeze then the output is:

pvs --noheadings --nosuffix --units=m --unbuffered '--separator=|' -opv_name,vg_name,pv_free,pv_attr

Spadaccio opened ganeti bug http://code.google.com/p/ganeti/issues/detail?id=207

Switching back and forth between lvm2_2.02.66-5_amd64.deb  lvm2_2.02.88-2_amd64.deb
from squeeze and wheezy made no difference, the bug is repeatable _FOR_ me. Not for Spadaccio.

The difference between our setups might be that his xenvg VolumeGroup is first and mine is 2.
after a system volume group.

root at ugcn1:~# pvs --noheadings --nosuffix --units=m --unbuffered '--separator=|' -opv_name,vg_name,pv_free,pv_attr

I created my wheezy installation by installing from a debian squeeze netinstall cd image which
I then did an apt-get dist-upgrade to wheezy.

-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.1.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages lvm2 depends on:
ii  dmsetup             2:1.02.67-2  
ii  initscripts         2.88dsf-13.13
ii  libc6               2.13-21      
ii  libdevmapper1.02.1  2:1.02.67-2  
ii  libreadline5        5.2-11       
ii  libudev0            175-2        
ii  lsb-base            3.2-28       

lvm2 recommends no packages.

lvm2 suggests no packages.

-- Configuration Files:
/etc/lvm/lvm.conf changed:
devices {
    # Where do you want your volume groups to appear ?
    dir = "/dev"
    # An array of directories that contain the device nodes you wish
    # to use with LVM2.
    scan = [ "/dev" ]
    # If set, the cache of block device nodes with all associated symlinks
    # will be constructed out of the existing udev database content.
    # This avoids using and opening any inapplicable non-block devices or
    # subdirectories found in the device directory. This setting is applied
    # to udev-managed device directory only, other directories will be scanned
    # fully. LVM2 needs to be compiled with udev support for this setting to
    # take effect. N.B. Any device node or symlink not managed by udev in
    # udev directory will be ignored with this setting on.
    obtain_device_list_from_udev = 1
    # If several entries in the scanned directories correspond to the
    # same block device and the tools need to display a name for device,
    # all the pathnames are matched against each item in the following
    # list of regular expressions in turn and the first match is used.
    preferred_names = [ ]
    # Try to avoid using undescriptive /dev/dm-N names, if present.
    # preferred_names = [ "^/dev/mpath/", "^/dev/mapper/mpath", "^/dev/[hs]d" ]
    # A filter that tells LVM2 to only use a restricted set of devices.
    # The filter consists of an array of regular expressions.  These
    # expressions can be delimited by a character of your choice, and
    # prefixed with either an 'a' (for accept) or 'r' (for reject).
    # The first expression found to match a device name determines if
    # the device will be accepted or rejected (ignored).  Devices that
    # don't match any patterns are accepted.
    # Be careful if there there are symbolic links or multiple filesystem 
    # entries for the same device as each name is checked separately against
    # the list of patterns.  The effect is that if any name matches any 'a'
    # pattern, the device is accepted; otherwise if any name matches any 'r'
    # pattern it is rejected; otherwise it is accepted.
    # Don't have more than one filter line active at once: only one gets used.
    # Run vgscan after you change this parameter to ensure that
    # the cache file gets regenerated (see below).
    # If it doesn't do what you expect, check the output of 'vgscan -vvvv'.
    # By default we accept every block device:
    filter = [ "r|/dev/drbd.*|", "a/.*/" ]
    # Exclude the cdrom drive
    # filter = [ "r|/dev/cdrom|" ]
    # When testing I like to work with just loopback devices:
    # filter = [ "a/loop/", "r/.*/" ]
    # Or maybe all loops and ide drives except hdc:
    # filter =[ "a|loop|", "r|/dev/hdc|", "a|/dev/ide|", "r|.*|" ]
    # Use anchors if you want to be really specific
    # filter = [ "a|^/dev/hda8$|", "r/.*/" ]
    # The results of the filtering are cached on disk to avoid
    # rescanning dud devices (which can take a very long time).
    # By default this cache is stored in the /etc/lvm/cache directory
    # in a file called '.cache'.
    # It is safe to delete the contents: the tools regenerate it.
    # (The old setting 'cache' is still respected if neither of
    # these new ones is present.)
    cache_dir = "/run/lvm"
    cache_file_prefix = ""
    # You can turn off writing this cache file by setting this to 0.
    write_cache_state = 1
    # Advanced settings.
    # List of pairs of additional acceptable block device types found 
    # in /proc/devices with maximum (non-zero) number of partitions.
    # types = [ "fd", 16 ]
    # If sysfs is mounted (2.6 kernels) restrict device scanning to 
    # the block devices it believes are valid.
    # 1 enables; 0 disables.
    sysfs_scan = 1
    # By default, LVM2 will ignore devices used as components of
    # software RAID (md) devices by looking for md superblocks.
    # 1 enables; 0 disables.
    md_component_detection = 1
    # By default, if a PV is placed directly upon an md device, LVM2
    # will align its data blocks with the md device's stripe-width.
    # 1 enables; 0 disables.
    md_chunk_alignment = 1
    # Default alignment of the start of a data area in MB.  If set to 0,
    # a value of 64KB will be used.  Set to 1 for 1MiB, 2 for 2MiB, etc.
    # default_data_alignment = 1
    # By default, the start of a PV's data area will be a multiple of
    # the 'minimum_io_size' or 'optimal_io_size' exposed in sysfs.
    # - minimum_io_size - the smallest request the device can perform
    #   w/o incurring a read-modify-write penalty (e.g. MD's chunk size)
    # - optimal_io_size - the device's preferred unit of receiving I/O
    #   (e.g. MD's stripe width)
    # minimum_io_size is used if optimal_io_size is undefined (0).
    # If md_chunk_alignment is enabled, that detects the optimal_io_size.
    # This setting takes precedence over md_chunk_alignment.
    # 1 enables; 0 disables.
    data_alignment_detection = 1
    # Alignment (in KB) of start of data area when creating a new PV.
    # md_chunk_alignment and data_alignment_detection are disabled if set.
    # Set to 0 for the default alignment (see: data_alignment_default)
    # or page size, if larger.
    data_alignment = 0
    # By default, the start of the PV's aligned data area will be shifted by
    # the 'alignment_offset' exposed in sysfs.  This offset is often 0 but
    # may be non-zero; e.g.: certain 4KB sector drives that compensate for
    # windows partitioning will have an alignment_offset of 3584 bytes
    # (sector 7 is the lowest aligned logical block, the 4KB sectors start
    # at LBA -1, and consequently sector 63 is aligned on a 4KB boundary).
    # But note that pvcreate --dataalignmentoffset will skip this detection.
    # 1 enables; 0 disables.
    data_alignment_offset_detection = 1
    # If, while scanning the system for PVs, LVM2 encounters a device-mapper
    # device that has its I/O suspended, it waits for it to become accessible.
    # Set this to 1 to skip such devices.  This should only be needed
    # in recovery situations.
    ignore_suspended_devices = 0
    # During each LVM operation errors received from each device are counted.
    # If the counter of a particular device exceeds the limit set here, no
    # further I/O is sent to that device for the remainder of the respective
    # operation. Setting the parameter to 0 disables the counters altogether.
    disable_after_error_count = 0
    # Allow use of pvcreate --uuid without requiring --restorefile.
    require_restorefile_with_uuid = 1
    # Minimum size (in KB) of block devices which can be used as PVs.
    # In a clustered environment all nodes must use the same value.
    # Any value smaller than 512KB is ignored.
    # Ignore devices smaller than 2MB such as floppy drives.
    pv_min_size = 2048
    # The original built-in setting was 512 up to and including version 2.02.84.
    # pv_min_size = 512
    # Issue discards to a logical volumes's underlying physical volume(s) when
    # the logical volume is no longer using the physical volumes' space (e.g.
    # lvremove, lvreduce, etc).  Discards inform the storage that a region is
    # no longer in use.  Storage that supports discards advertise the protocol
    # specific way discards should be issued by the kernel (TRIM, UNMAP, or
    # WRITE SAME with UNMAP bit set).  Not all storage will support or benefit
    # from discards but SSDs and thinly provisioned LUNs generally do.  If set
    # to 1, discards will only be issued if both the storage and kernel provide
    # support.
    # 1 enables; 0 disables.
    issue_discards = 0
log {
    # Controls the messages sent to stdout or stderr.
    # There are three levels of verbosity, 3 being the most verbose.
    verbose = 0
    # Should we send log messages through syslog?
    # 1 is yes; 0 is no.
    syslog = 1
    # Should we log error and debug messages to a file?
    # By default there is no log file.
    #file = "/var/log/lvm2.log"
    # Should we overwrite the log file each time the program is run?
    # By default we append.
    overwrite = 0
    # What level of log messages should we send to the log file and/or syslog?
    # There are 6 syslog-like log levels currently in use - 2 to 7 inclusive.
    # 7 is the most verbose (LOG_DEBUG).
    level = 0
    # Format of output messages
    # Whether or not (1 or 0) to indent messages according to their severity
    indent = 1
    # Whether or not (1 or 0) to display the command name on each line output
    command_names = 0
    # A prefix to use before the message text (but after the command name,
    # if selected).  Default is two spaces, so you can see/grep the severity
    # of each message.
    prefix = "  "
    # To make the messages look similar to the original LVM tools use:
    #   indent = 0
    #   command_names = 1
    #   prefix = " -- "
    # Set this if you want log messages during activation.
    # Don't use this in low memory situations (can deadlock).
    # activation = 0
backup {
    # Should we maintain a backup of the current metadata configuration ?
    # Use 1 for Yes; 0 for No.
    # Think very hard before turning this off!
    backup = 1
    # Where shall we keep it ?
    # Remember to back up this directory regularly!
    backup_dir = "/etc/lvm/backup"
    # Should we maintain an archive of old metadata configurations.
    # Use 1 for Yes; 0 for No.
    # On by default.  Think very hard before turning this off.
    archive = 1
    # Where should archived files go ?
    # Remember to back up this directory regularly!
    archive_dir = "/etc/lvm/archive"
    # What is the minimum number of archive files you wish to keep ?
    retain_min = 10
    # What is the minimum time you wish to keep an archive file for ?
    retain_days = 30
shell {
    # Number of lines of history to store in ~/.lvm_history
    history_size = 100
global {
    # The file creation mask for any files and directories created.
    # Interpreted as octal if the first digit is zero.
    umask = 077
    # Allow other users to read the files
    #umask = 022
    # Enabling test mode means that no changes to the on disk metadata
    # will be made.  Equivalent to having the -t option on every
    # command.  Defaults to off.
    test = 0
    # Default value for --units argument
    units = "h"
    # Since version 2.02.54, the tools distinguish between powers of
    # 1024 bytes (e.g. KiB, MiB, GiB) and powers of 1000 bytes (e.g.
    # KB, MB, GB).
    # If you have scripts that depend on the old behaviour, set this to 0
    # temporarily until you update them.
    si_unit_consistency = 1
    # Whether or not to communicate with the kernel device-mapper.
    # Set to 0 if you want to use the tools to manipulate LVM metadata 
    # without activating any logical volumes.
    # If the device-mapper kernel driver is not present in your kernel
    # setting this to 0 should suppress the error messages.
    activation = 1
    # If we can't communicate with device-mapper, should we try running 
    # the LVM1 tools?
    # This option only applies to 2.4 kernels and is provided to help you
    # switch between device-mapper kernels and LVM1 kernels.
    # The LVM1 tools need to be installed with .lvm1 suffices
    # e.g. vgscan.lvm1 and they will stop working after you start using
    # the new lvm2 on-disk metadata format.
    # The default value is set when the tools are built.
    # fallback_to_lvm1 = 0
    # The default metadata format that commands should use - "lvm1" or "lvm2".
    # The command line override is -M1 or -M2.
    # Defaults to "lvm2".
    # format = "lvm2"
    # Location of proc filesystem
    proc = "/proc"
    # Type of locking to use. Defaults to local file-based locking (1).
    # Turn locking off by setting to 0 (dangerous: risks metadata corruption
    # if LVM2 commands get run concurrently).
    # Type 2 uses the external shared library locking_library.
    # Type 3 uses built-in clustered locking.
    # Type 4 uses read-only locking which forbids any operations that might 
    # change metadata.
    locking_type = 1
    # Set to 0 to fail when a lock request cannot be satisfied immediately.
    wait_for_locks = 1
    # If using external locking (type 2) and initialisation fails,
    # with this set to 1 an attempt will be made to use the built-in
    # clustered locking.
    # If you are using a customised locking_library you should set this to 0.
    fallback_to_clustered_locking = 1
    # If an attempt to initialise type 2 or type 3 locking failed, perhaps
    # because cluster components such as clvmd are not running, with this set
    # to 1 an attempt will be made to use local file-based locking (type 1).
    # If this succeeds, only commands against local volume groups will proceed.
    # Volume Groups marked as clustered will be ignored.
    fallback_to_local_locking = 1
    # Local non-LV directory that holds file-based locks while commands are
    # in progress.  A directory like /tmp that may get wiped on reboot is OK.
    locking_dir = "/run/lock/lvm"
    # Whenever there are competing read-only and read-write access requests for
    # a volume group's metadata, instead of always granting the read-only
    # requests immediately, delay them to allow the read-write requests to be
    # serviced.  Without this setting, write access may be stalled by a high
    # volume of read-only requests.
    # NB. This option only affects locking_type = 1 viz. local file-based
    # locking.
    prioritise_write_locks = 1
    # Other entries can go here to allow you to load shared libraries
    # e.g. if support for LVM1 metadata was compiled as a shared library use
    #   format_libraries = "liblvm2format1.so" 
    # Full pathnames can be given.
    # Search this directory first for shared libraries.
    #   library_dir = "/lib/lvm2"
    # The external locking library to load if locking_type is set to 2.
    #   locking_library = "liblvm2clusterlock.so"
    # Treat any internal errors as fatal errors, aborting the process that
    # encountered the internal error. Please only enable for debugging.
    abort_on_internal_errors = 0
    # Check whether CRC is matching when parsed VG is used multiple times.
    # This is useful to catch unexpected internal cached volume group
    # structure modification. Please only enable for debugging.
    detect_internal_vg_cache_corruption = 0
    # If set to 1, no operations that change on-disk metadata will be permitted.
    # Additionally, read-only commands that encounter metadata in need of repair
    # will still be allowed to proceed exactly as if the repair had been 
    # performed (except for the unchanged vg_seqno).
    # Inappropriate use could mess up your system, so seek advice first!
    metadata_read_only = 0
    # 'mirror_segtype_default' defines which segtype will be used when the
    # shorthand '-m' option is used for mirroring.  The possible options are:
    # "mirror" - The original RAID1 implementation provided by LVM2/DM.  It is
    # 	         characterized by a flexible log solution (core, disk, mirrored)
    #		 and by the necessity to block I/O while reconfiguring in the
    #		 event of a failure.  Snapshots of this type of RAID1 can be
    #		 problematic.
    # "raid1"  - This implementation leverages MD's RAID1 personality through
    # 	       	 device-mapper.  It is characterized by a lack of log options.
    #		 (A log is always allocated for every device and they are placed
    #		 on the same device as the image - no separate devices are
    #		 required.)  This mirror implementation does not require I/O
    #		 to be blocked in the kernel in the event of a failure.
    # Specify the '--type <mirror|raid1>' option to override this default
    # setting.
    mirror_segtype_default = "mirror"
activation {
    # Set to 1 to perform internal checks on the operations issued to
    # libdevmapper.  Useful for debugging problems with activation.
    # Some of the checks may be expensive, so it's best to use this
    # only when there seems to be a problem.
    checks = 0
    # Set to 0 to disable udev synchronisation (if compiled into the binaries).
    # Processes will not wait for notification from udev.
    # They will continue irrespective of any possible udev processing
    # in the background.  You should only use this if udev is not running
    # or has rules that ignore the devices LVM2 creates.
    # The command line argument --nodevsync takes precedence over this setting.
    # If set to 1 when udev is not running, and there are LVM2 processes
    # waiting for udev, run 'dmsetup udevcomplete_all' manually to wake them up.
    udev_sync = 1
    # Set to 0 to disable the udev rules installed by LVM2 (if built with
    # --enable-udev_rules). LVM2 will then manage the /dev nodes and symlinks
    # for active logical volumes directly itself.
    # N.B. Manual intervention may be required if this setting is changed
    # while any logical volumes are active.
    udev_rules = 1
    # Set to 1 for LVM2 to verify operations performed by udev. This turns on
    # additional checks (and if necessary, repairs) on entries in the device
    # directory after udev has completed processing its events. 
    # Useful for diagnosing problems with LVM2/udev interactions.
    verify_udev_operations = 0
    # How to fill in missing stripes if activating an incomplete volume.
    # Using "error" will make inaccessible parts of the device return
    # I/O errors on access.  You can instead use a device path, in which 
    # case, that device will be used to in place of missing stripes.
    # But note that using anything other than "error" with mirrored 
    # or snapshotted volumes is likely to result in data corruption.
    missing_stripe_filler = "error"
    # How much stack (in KB) to reserve for use while devices suspended
    reserved_stack = 256
    # How much memory (in KB) to reserve for use while devices suspended
    reserved_memory = 8192
    # Nice value used while devices suspended
    process_priority = -18
    # If volume_list is defined, each LV is only activated if there is a
    # match against the list.
    #   "vgname" and "vgname/lvname" are matched exactly.
    #   "@tag" matches any tag set in the LV or VG.
    #   "@*" matches if any tag defined on the host is also set in the LV or VG
    # volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]
    # Size (in KB) of each copy operation when mirroring
    mirror_region_size = 512
    # Setting to use when there is no readahead value stored in the metadata.
    # "none" - Disable readahead.
    # "auto" - Use default value chosen by kernel.
    readahead = "auto"
    # 'mirror_image_fault_policy' and 'mirror_log_fault_policy' define
    # how a device failure affecting a mirror is handled.
    # A mirror is composed of mirror images (copies) and a log.
    # A disk log ensures that a mirror does not need to be re-synced
    # (all copies made the same) every time a machine reboots or crashes.
    # In the event of a failure, the specified policy will be used to determine
    # what happens. This applies to automatic repairs (when the mirror is being
    # monitored by dmeventd) and to manual lvconvert --repair when
    # --use-policies is given.
    # "remove" - Simply remove the faulty device and run without it.  If
    #            the log device fails, the mirror would convert to using
    #            an in-memory log.  This means the mirror will not
    #            remember its sync status across crashes/reboots and
    #            the entire mirror will be re-synced.  If a
    #            mirror image fails, the mirror will convert to a
    #            non-mirrored device if there is only one remaining good
    #            copy.
    # "allocate" - Remove the faulty device and try to allocate space on
    #            a new device to be a replacement for the failed device.
    #            Using this policy for the log is fast and maintains the
    #            ability to remember sync state through crashes/reboots.
    #            Using this policy for a mirror device is slow, as it
    #            requires the mirror to resynchronize the devices, but it
    #            will preserve the mirror characteristic of the device.
    #            This policy acts like "remove" if no suitable device and
    #            space can be allocated for the replacement.
    # "allocate_anywhere" - Not yet implemented. Useful to place the log device
    #            temporarily on same physical volume as one of the mirror
    #            images. This policy is not recommended for mirror devices
    #            since it would break the redundant nature of the mirror. This
    #            policy acts like "remove" if no suitable device and space can
    #            be allocated for the replacement.
    mirror_log_fault_policy = "allocate"
    mirror_image_fault_policy = "remove"
    # 'snapshot_autoextend_threshold' and 'snapshot_autoextend_percent' define
    # how to handle automatic snapshot extension. The former defines when the
    # snapshot should be extended: when its space usage exceeds this many
    # percent. The latter defines how much extra space should be allocated for
    # the snapshot, in percent of its current size.
    # For example, if you set snapshot_autoextend_threshold to 70 and
    # snapshot_autoextend_percent to 20, whenever a snapshot exceeds 70% usage,
    # it will be extended by another 20%. For a 1G snapshot, using up 700M will
    # trigger a resize to 1.2G. When the usage exceeds 840M, the snapshot will
    # be extended to 1.44G, and so on.
    # Setting snapshot_autoextend_threshold to 100 disables automatic
    # extensions. The minimum value is 50 (A setting below 50 will be treated
    # as 50).
    snapshot_autoextend_threshold = 100
    snapshot_autoextend_percent = 20
    # While activating devices, I/O to devices being (re)configured is
    # suspended, and as a precaution against deadlocks, LVM2 needs to pin
    # any memory it is using so it is not paged out.  Groups of pages that
    # are known not to be accessed during activation need not be pinned
    # into memory.  Each string listed in this setting is compared against
    # each line in /proc/self/maps, and the pages corresponding to any
    # lines that match are not pinned.  On some systems locale-archive was
    # found to make up over 80% of the memory used by the process.
    # mlock_filter = [ "locale/locale-archive", "gconv/gconv-modules.cache" ]
    # Set to 1 to revert to the default behaviour prior to version 2.02.62
    # which used mlockall() to pin the whole process's memory while activating
    # devices.
    use_mlockall = 0
    # Monitoring is enabled by default when activating logical volumes.
    # Set to 0 to disable monitoring or use the --ignoremonitoring option.
    monitoring = 1
    # When pvmove or lvconvert must wait for the kernel to finish
    # synchronising or merging data, they check and report progress
    # at intervals of this number of seconds.  The default is 15 seconds.
    # If this is set to 0 and there is only one thing to wait for, there
    # are no progress reports, but the process is awoken immediately the
    # operation is complete.
    polling_interval = 15
    # Default number of copies of metadata to hold on each PV.  0, 1 or 2.
    # You might want to override it from the command line with 0 
    # when running pvcreate on new PVs which are to be added to large VGs.
    # pvmetadatacopies = 1
    # Default number of copies of metadata to maintain for each VG.
    # If set to a non-zero value, LVM automatically chooses which of
    # the available metadata areas to use to achieve the requested
    # number of copies of the VG metadata.  If you set a value larger
    # than the the total number of metadata areas available then
    # metadata is stored in them all.
    # The default value of 0 ("unmanaged") disables this automatic
    # management and allows you to control which metadata areas
    # are used at the individual PV level using 'pvchange
    # --metadataignore y/n'.
    # vgmetadatacopies = 0
    # Approximate default size of on-disk metadata areas in sectors.
    # You should increase this if you have large volume groups or
    # you want to retain a large on-disk history of your metadata changes.
    # pvmetadatasize = 255
    # List of directories holding live copies of text format metadata.
    # These directories must not be on logical volumes!
    # It's possible to use LVM2 with a couple of directories here,
    # preferably on different (non-LV) filesystems, and with no other 
    # on-disk metadata (pvmetadatacopies = 0). Or this can be in
    # addition to on-disk metadata areas.
    # The feature was originally added to simplify testing and is not
    # supported under low memory situations - the machine could lock up.
    # Never edit any files in these directories by hand unless you
    # you are absolutely sure you know what you are doing! Use
    # the supplied toolset to make changes (e.g. vgcfgrestore).
    # dirs = [ "/etc/lvm/metadata", "/mnt/disk2/lvm/metadata2" ]
dmeventd {
    # mirror_library is the library used when monitoring a mirror device.
    # "libdevmapper-event-lvm2mirror.so" attempts to recover from
    # failures.  It removes failed devices from a volume group and
    # reconfigures a mirror as necessary. If no mirror library is
    # provided, mirrors are not monitored through dmeventd.
    mirror_library = "libdevmapper-event-lvm2mirror.so"
    # snapshot_library is the library used when monitoring a snapshot device.
    # "libdevmapper-event-lvm2snapshot.so" monitors the filling of
    # snapshots and emits a warning through syslog when the use of
    # the snapshot exceeds 80%. The warning is repeated when 85%, 90% and
    # 95% of the snapshot is filled.
    snapshot_library = "libdevmapper-event-lvm2snapshot.so"
    # Full path of the dmeventd binary.
    # executable = ""

-- no debconf information

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