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Special Forums Hardware Filesystems, Disks and Memory Faster way: SAN hd to SAN hd copying Post 303007674 by rbatte1 on Monday 20th of November 2017 05:57:48 AM
Old 11-20-2017
When you say 'a faster way', are you trying to move the data from one SAN to another, so that you can detach the original and you need to make the offline time as short as possible?

If your disk is LVM, then you might be better to proceed like this:-
  • Get the new LUN assigned and re-scan to pick it up if necessary
  • Make the whole new LUN into an LVM Physical Volume with pvcreate
  • Add the PV into the volume group containing the data you want to move
  • Alter the logical volume holding your filesystem/data to have two copies, specifying the new PV as the target. This will take a long time, but the applications remain available because the data is still accessible.
  • Verify that the logical volume has no errors reported.
  • Alter the logical volume to have just a single copy, specifying the old SAN device to be removed
  • Repeat the mirror/drop for as many logical volumes as you need to move to completely free the old PV
  • Remove the old PV from the volume group
  • Detach the old LUN from the OS
  • Detach the old LUN from the SAN side

Using the tools in the OS rather than trying to do the work yourself should be a lot neater. The logical volume is moved, but the filesystem has no idea about it, so all the files remain exactly as they were and your applications, backups or whatever can happily carry on.

I prefer to add a mirror to the new device rather than just execute a move for large logical volumes just in case there are any issues in the process. You don't destroy the original so you can always drop the new copy and start again.


Have I missed the point and waffled on about something irrelevant? My apologies if I have, but I hope that this helps. If you are looking to make another copy to be used separately, then we might be able to use LVM to do that too, but that would be a copy at a fixed point in time that would then go out of date with respect to the original as either is changed (you suggest that there are many concurrent processes working on it)


Anyway, I hope that this helps. Please feel free to correct me if I'm way off target.


Kind regards,
Robin
 

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PVMOVE(8)						      System Manager's Manual							 PVMOVE(8)

NAME
pvmove - move physical extents SYNOPSIS
pvmove [--abort] [--alloc AllocationPolicy] [-b|--background] [-d|--debug] [-h|--help] [-i|--interval Seconds] [--noudevsync] [-v|--ver- bose] [-n|--name LogicalVolume] [SourcePhysicalVolume[:PE[-PE]...] [DestinationPhysicalVolume[:PE[-PE]...]...]] DESCRIPTION
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 DestinationPhysicalVolume 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 PhysicalVolume 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 check- point. 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-allocated 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 mir- rored 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 temporary 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 converted using vgconvert(8). OPTIONS
--abort Abort any moves in progress. --noudevsync 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 cre- ates. -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 phys- ical volume(s). EXAMPLES
To move all logical extents of any logical volumes on /dev/hda4 to free physical extents elsewhere in the volume group, giving verbose run- time information, use: pvmove -v /dev/hda4 SEE ALSO
lvm(8), vgconvert(8) Sistina Software UK LVM TOOLS 2.02.67(2) (2010-06-04) PVMOVE(8)
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