Moving Striped LV's with LVExtend & LVReduce

[Andrew S Babb]

I was wondering if there is a way to move an LV that was create with a stripe witdth of 4 disks to another set of disks, using LVExtend / LVReduce.

Our problem is that we have to move out DW from one Symmetrix frame to another, we have outgrown the first frame, and rather than exporting the data, creating the database on the new frame, and then importing the data, could we use LVExtend to create a second copy of the LV on the new frame, and then LVReduce to remove the original copy from the old frame.

Generally, we would keep the same strip width, if it is 4 disk on the old frame, it will be 4 disk on the new frame, but would it be possible to change the stripe size to 8 disks?

TIA
Andrew

[Steven Sim Kok Leong]

Hi,

Is there an equivalent of Auto LUN for EMC Symmetrix as there is for HP's XP256/XP512? I have not experienced it personally myself.

However, I was told that Auto LUN in XP256/XP512 allows you to manually and in a controlled manner shift LUNs among different physical locations in the frames and among different RAID groups with the option of converting between different RAID levels.

Since Auto LUN allows you to shift LUNs around at the LUN level with RAID conversion, it might be suitable for your need in changing the number of stripes across disks in your RAID group in a more easy way.

Hope this helps. Regards.

Steven Sim
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Andrew S Babb]

Although EMC does have the facility to move LUN's around within a particular frame, they cannot move LUN's between frames.

I believe the only option I have is to use LVExtend and LVReduce

Thanks

[Wodisch]

Hello Andrew,

have you considered using "pvmove"? It is a supported
tool, and I actually have move whole SAP R/3 databases
around - without stopping Oracle nor SAP!
Since you have EMC, I do guess you are doing the
striping on the EMC (as BVC, or so), so you will not
run into any problems with LVM striping and mirroring...
HTH,
Wodisch

[Andrew S Babb]

Hi,

On EMC the hardware striping is not very kind, 1Mb stripe size, and also we would have to specify this when EMC configure the box, and it cannot be changed at a later time.

Therefore, we are using LVM to perform the striping. I guess pvmove (I need to look into it) could move 1/4 of the stripe from an old disk to a new disk, but we could not change our striping policy, i.e. 4 old disks to 8 new disks.

Additional Information, the reason for the move to the new EMC frame is to support a 3 fold increase in the size of the target database.

Thanks
Andrew

[Steven Sim Kok Leong]

Hi,

If you are looking at striping at the hardware level, if you have BCV, you can shutdown your application, execute a BC split, reconfigure your RAID 5 group to the correct stripe settings, and subsequently synchronise back from your BCV.

If you are looking at striping at the OS level, the cleaniest way to modify the number of stripes across disks would be shutting down your applications, followed by a full system backup, subsequently creation of the appropriate striped LVs and restoration of data from backup. As far as I know, there is no other alternative to this with LVM.

Both methods should allow you to reconfigure the number of disks you wish to stripe across.

Hope this helps. Regards.

Steven Sim
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Andrew S Babb]

We do not have enough storage to support an entire or partial BCV configuration, and also, to my understanding, BCV's only work in the same EMC Frame.

We are considering as a last resort the shutdown of the database, and effectively a DD from the source to the target LV position, but would like to use LVExtend / LVReduce so that we do not have to down the system for any period of time.

Andrew

[Tim Malnati · Accepted solution]

Where you are moving from one frame to another there is little choice but to rebuild them. There are a variety of methods of getting the data from here to there but having physical connections to both frames at the same time will be the fastest. Pvmove will not help in this situation where you are looking to change the volume geopmetry. Rdist can drastically reduce outage time though (do a search on my previous posts for more info).

You mention 1MB stripes. Are you doing extent striping? There is no need for doing this with an EMC where the redundancy is handled at the hardware. If you attempting to stripe raid S you are wasting your time and could be negatively impacting your throughput. Different story with full mirrored volumes though (and a big increase in throughput). EMC should have 32K stripes where this is the internal block size of the hardware. Use lvcreate -i 8 -I 32 ... for an eight way set. The only time that these options are locked out is when you are creating LVM mirrors which is not the preferred way of doing it with an EMC. If you want additional mirror sets use EMC's TimeFinder product instead. This allows you much more control of any mirrors and many more connection possibilities. For instance, you can split off a mirror and mount it to a totally different machine. Also, EMC will not require that the additional BCV volumes be fully redundant within the frame either (save some disk).

[Andrew S Babb]

The only method of Hardware Stiping in EMC that I am aware is the concept of Meta Volumes. With the configuration that we have, i've been told that the stripe size is 1Mb and not 32K. Also, this is a BIN file configuration requirement, and we are still configuring our DW.

BTW - What we are doing is striping over 4 or 8 different Raid-S groups, 1 disk per Raid-S group, which are known to be on different Disk Directors (Disk Controllers) and also spread between 2 different Channel Directors (Fiber Channel Controllers).

From reading the reply, it looks like I will not be able to use the LVExtend / LVReduce approach due to the fact that we can only use LVM striping when we are not using LVM mirroring.

Thanks
Andrew

[Dave Wherry]

If both of your Symmetrex' are connected to the host, and your database is created on file system (cooked) not raw space, simply create a new volume group and logical volumes on your new disks, using your new stripe layout. Shutdown your database. Copy the data from the old to the new. Unmount the old and new. Edit your /etc/fstab to make the new become the old. Mount it and you are done.
Depending on the size of your database this could take some time. However it's much faster than backing up and restoring. It's 1 step rather than 2.