topic Re: lvreduce and lvextend in Operating System - HP-UX

lvreduce and lvextend

john schiwitz — Fri, 17 Oct 2003 08:57:22 GMT

I am moving lvs from one disk to another using lvextend newdisk and lvreduce olddisk/primary mirror. A HP engineer told me that I would have to umount the lvs prior to lvreduce or I would risk filesystem corruption. I trust the HP engineer but my response was, "what good is OnlineJFS"?

I don't have to do this on AIX ;->>

Is this an old lvm bug or just a design feature? Has anyone else heard of this feature/recommendation?

Re: lvreduce and lvextend

Pete Randall — Fri, 17 Oct 2003 09:01:17 GMT

John,

I don't see where OnlineJFS comes into this. You're adding a mirror with lvextend, then using lvreduce to get rid of the original primary? That involves MirrorDisk/UX, not OnlineJFS - and I may be wrong, but I don't think you have to unmount the filesystem.

Pete

Re: lvreduce and lvextend

Bryan D. Quinn — Fri, 17 Oct 2003 09:09:40 GMT

Hello,

I would have to agree with Pete, I don't see where umounting or the use of OnlineJFS has anything to do with this.

Say these are your disks:

c0t1d0 old disk
c0t2d0 new disk

You should be able to do this:

lvextend -m 1 /dev/vgXX/lvolX /dev/dsk/c0t2d0

Then do:

lvreduce -m 0 /dev/vgXX/lvolX /dev/dsk/c0t1d0

I would think that would be all you need to do.

Hope this helps!
-Bryan

Re: lvreduce and lvextend

G. Vrijhoeven — Fri, 17 Oct 2003 09:09:52 GMT

Hi,

lvreduce is to reduce lvols and online jfs works with filesystems.

1 add the now disk to the volumegroup
pvcreate /dev/rdsk/c?t?d? && vgextend /dev/vg?? /dev/dsk/c?t?d?
2 add a mirrorcopy to the lvols
lvextend -m1 /dev/vg??/lvol? /dev/dsk/c?t?d?
3. lvreduce the old disk
lvreduce -m0 /dev/vg??/lvol? /dev/dsk/c?t?d?
4. remove the disk out of the volume group
vgreduce /dev/vg?? /dev/dsk/c?t?d?

There is no need voor onlinejfs.

If you do need to use it just fsadm -F vxfs -b /mountpoint is safe if you have enough free space.

Gideon

Gideon

It is safe to use lvreduce

Re: lvreduce and lvextend

Patrick Wallek — Fri, 17 Oct 2003 09:35:11 GMT

The way you are diong it will work. But an easier way is to use pvmove. pvmove will do what you are doing automatically.

There isn't any reason to unmount the LV prior to lvreducing.

Re: lvreduce and lvextend

Todd McDaniel_1 — Fri, 17 Oct 2003 10:49:01 GMT

I am inclined to go with the mirroring solution... more straight forward IMHO.

lvextend -m 1 /dev/vgXX /dev/dsk/cXtXdX for new mirror on new disk

lvreduce -m 0 /dev/vgXX /dev/dsk/cXtXdX for removal of old disk

Then remove the old disk from the VG or reallocate it.

Re: lvreduce and lvextend

john schiwitz — Fri, 17 Oct 2003 12:48:46 GMT

oops I meant mirrorux not onlinejfs.

I've lvextended and lvreduced hundreds of times without any problems.

But the HP support team says I quote:
"

It is critical to ensure that all I/O has been flushed to both copies of
the mirrored logical volume(s) before reducing one of the mirror copies;
the only way to guarantee this is to stop the application, unmount the
filesystems or raw volumes, and deactivate the volume groups that are
affected

NOTE: these steps need to be done on all 9 systems, however they can
be performed one system at a time if desired

a) Confirm mirrors are sync'd before proceeding

# vgdisplay -v (ensure all LVs are sync'd)

b) Ensure the I/O is flushed to each logical volume

Stop application
umount filesystems
deactivate VGs

# vgdisplay (only vg00 should be active)

c) Reduce a mirror from each logical volume

# vgchange -a y /dev/vgxx
# vgdisplay -v

# lvreduce -m 0 /dev/VGxx/LVx /dev/dsk/...
# lvdisplay -v /dev/VGxx/LVx

# vgreduce /dev/VGxx /dev/dsk/... (alternate link)
# vgreduce /dev/VGxx /dev/dsk/... (primary link)
# vgdisplay -v /dev/VG
# strings /etc/lvmtab
"

They say if you really want to do this with your filesystems active you need to buy vxvm.

Just wondered if anyone else had heard this feature with lvreduce/lvextend?