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  1. #1

    How stable is pvmove


    I need to move a VG of 2.1TB from one storage to another storage in production so pvmove is safer to use and does it copy the data from one storage to another or it move the data ??

    And in some forums mentioned like pvmove may damage VG so i am worried to use this command.Please suggest..


  2. #2
    Linux Guru Rubberman's Avatar
    Join Date
    Apr 2009
    I can be found either 40 miles west of Chicago, in Chicago, or in a galaxy far, far away.
    Have you read the man page? In any case, it physically moves extents from one device to another.

    Here is a copy of the man page from my RHEL 6.1 system:

    PVMOVE(8)                                                            PVMOVE(8)
           pvmove - move physical extents
           pvmove  [--abort] [--alloc AllocationPolicy] [-b|--background] [-d|--debug] [-h|--help] [-i|--interval Seconds]
           [--noudevsync] [-v|--verbose] [-n|--name LogicalVolume]  [SourcePhysicalVolume[:PE[-PE]...]  [DestinationPhysi-
           pvmove  allows  you  to  move the allocated physical extents (PEs) on SourcePhysicalVolume to one or more other
           physical volumes (PVs).  You can optionally specify a source LogicalVolume in which case only extents  used  by
           that  LV will be moved to free (or specified) extents on DestinationPhysicalVolume(s).  If no DestinationPhysi-
           calVolume is specifed, the normal allocation rules for the volume group are used.
           If pvmove gets interrupted for any reason (e.g. the machine crashes) then run pvmove again without  any  Physi-
           calVolume  arguments  to  restart  any moves that were in progress from the last checkpoint.  Alternatively use
           pvmove --abort at any time to abort them at the last checkpoint.
           You can run more than one pvmove at once provided they are moving data off different SourcePhysicalVolumes, but
           additional  pvmoves will ignore any logical volumes already in the process of being changed, so some data might
           not get moved.
           pvmove works as follows:
           1. A temporary ’pvmove’ logical volume is created to store details of all the data movements required.
           2. Every logical volume in the volume group is searched for contiguous data that need moving according  to  the
           command  line  arguments.   For  each  piece of data found, a new segment is added to the end of the pvmove LV.
           This segment takes the form of a temporary mirror to copy the data from the original location to a  newly-allo-
           cated location.  The original LV is updated to use the new temporary mirror segment in the pvmove LV instead of
           accessing the data directly.
           3. The volume group metadata is updated on disk.
           4. The first segment of the pvmove logical volume is activated and starts to mirror the first part of the data.
           Only one segment is mirrored at once as this is usually more efficient.
           5.  A  daemon repeatedly checks progress at the specified time interval.  When it detects that the first tempo-
           rary mirror is in-sync, it breaks that mirror so that only the new location for that data gets used and  writes
           a  checkpoint into the volume group metadata on disk.  Then it activates the mirror for the next segment of the
           pvmove LV.
           6. When there are no more segments left to be mirrored, the temporary logical volume is removed and the  volume
           group metadata is updated so that the logical volumes reflect the new data locations.
           Note  that  this  new  process cannot support the original LVM1 type of on-disk metadata.  Metadata can be con-
           verted using vgconvert(8).
                  Abort any moves in progress.
                  Disable udev synchronisation. The process will not wait for notification from udev.   It  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.
           -b, --background
                  Run the daemon in the background.
           -i, --interval Seconds
                  Report progress as a percentage at regular intervals.
           -n, --name  LogicalVolume
                  Move only the extents belonging to LogicalVolume from  SourcePhysicalVolume  instead  of  all  allocated
                  extents to the destination physical volume(s).
           To  move all logical extents of any logical volumes on /dev/hda4 to free physical extents elsewhere in the vol-
           ume group, giving verbose runtime information, use:
                pvmove -v /dev/hda4
           lvm(8), vgconvert(8)
    Sistina Software UK    LVM TOOLS 2.02.72(2) (2010-07-28)             PVMOVE(8)
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

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