Replacing LVM Disks

[Matthew Ghofrani]

L4000 with HPUX 11.0 with MC/ServiceGuard
EMC symmetrix box presenting 4 disks to the server for each physical spindle.
vxfs file system striped with several hot disks because they share the same spindle.

I can add identical disks for a short time, but I have to give back the same number. Is there a way to move off of just the hot disks? The application is critical and down time must be minimized.

[Krishna Prasad]

What do you mean by hot disks? Are you refering to an LVM mirror? or disk that is in use?

I am not sure I understand your question?

[Patrick Wallek]

If this is an EMC Symmetrix, can't you just replace the bad disk on the fly and have the EMC rebuild?

I am with Ron, I don't quite understand the question.

[Matthew Ghofrani]

Talked to EMC and they have no way to transfer the contents of a logical disk to another spindle. The disks I want to move from show significantly slower response than identical disks in the same volume group. EMC does show high activity on the physical disks which contain the group. I have more disks such that I can guarantee that a physical spindle is not host for more than one of the logical disks. This is a critical application (hospital) and I must minimize down time, so I'm looking for an alternative to backup, remove volume, recreate volume, restore data, that would be faster.

[Patrick Wallek]

When you say 'disks' on the EMC, I think you are really talking about the LUNs that are set up on the EMC?

That being the case, are you asking how to move the data, staying within the same VG, from one LUN to another?

If so, here is what I think you need to do:

# vgextend /dev/dsk/c?t?d? /dev/vg??

and add thew new LUNs from the EMC to your VG. Now you can use the pvmove command to move the extents from one LUN to another within that VG. See 'man pvmove' for more details.

# pvmove /dev/dsk/c1t2d3 /dev/dsk/c3t4d5

will move all extents from the c1t2d3 LUN to the c3t4d5 LUN.

# pvmove -n /dev/vg01/lvol2 /dev/dsk/c1t0d0 /dev/dsk/c2t0d0

Move only the physical extents for logical volume /dev/vg01/lvol2 that are currently on /dev/dsk/c1t0d0 to /dev/dsk/c2t0d0:

This can be done on-the-fly (I think), but be aware that this is a very disk intensive operation so your application response will slow down.

[Steven Gillard_2]

I take it you want to move data from one physical volume (LUN) to another? If so, the safest way is first to mirror on to the new PV's, then lvreduce off the old ones:

For each logical volume:
# lvextend -m 1
# lvreduce -m 0

Regards,
Steve

[Matthew Ghofrani]

Mirroring seems to be eliminated, because the logical volume is striped across everal LUNs. EMC has internal mirrors for each spindle, but I need to separate the 4 LUNs to be sure they are on separate spindles. EMC thinks this kind of ability to move a LUN might be valuable, but they have no way yet to do it with their software.

[Krishna Prasad]

I believe EMC does have a product that will move a LUN device to a different phyicall drive on the backend. This move is done transparent to the OS. It requires that you have some kind of BCV like device to temp. copy the data to. Then it copies it to a drive that is not to busy.

It is not an out of the box application. It does cost $$$.

In a non-related question why does my earlier response to this post have N/A as an option for pionts when I am not the author of this thread?

Sorry to cluter this thread with a forum issue.

[Krishna Prasad]

I believe the product name is work-load analyzer.

[Patrick Wallek]

Ron - you've got an N/A because that's what the author of the thread assigned you. Possible points assignments are N/A and 1-10 for each response.

[Matthew Ghofrani]

"Points are assigned on the value that an answer provides in helping solve the problem. Use the following scale, and then deviate inside the bands for answers that add more or less value:

N/A: The answer was simply a point of clarification to my original question"

I'm not very experienced with the system, yet, and was trying to follow directions.

Would dd be a tool I could use? If anybody's used this tool for disk to disk copy, what buffer size recommendations do you have?

[Patrick Wallek]

As I said already, use pvmove.

This will move the extents from one LUN to another. If you specify an LV and a device file, then it will just move the extents for that LV from one LUN to another. It should also keep you striping configuration as well.