Does LVM load balance on alternate paths?

[William Shaw]

Hello all, I'm just wondering if there is a
way to enable load balancing amoung multiple
paths to the same disk. I'm pretty sure that in a SUN environment, LVM does do I/O load balancing when there are mutilple paths to a single target. By default that doesn't appear to happen in HP-UX (11.00), but I was wondering if there's a way to enable this feature with HP-UX. thanks!

bill.shaw@hds.com

[James R. Ferguson]

William:

See this URL on the AutoRAID product. It does exactly what you want.

http://www.hp.com/cposupport/information_storage/support_doc/lpg75004.html

...JRF...

[Paula J Frazer-Campbell · Accepted solution]

Hi
Check out this thread

http://my1.itrc.hp.com/cm/QuestionAnswer/1,1150,0x54d7f841489fd4118fef0090279cd0f9,00.html

HTH
Paula

[William Shaw]

Thanks for the replies! The AutoRaid isn't quite what I was looking for, as there's no automatic I/O load balancing between multiple paths to a device/LUN. The thread from a couple of weeks ago is basically the same as my question above. I didn't see it the first time I browsed the subject lines.

Anyway thanks again,
Bill

[Paul McCleary]

Hi Will,

The AutoRAID could be what you're after if u set it up right.

A not too publisiced way, but still supported, is to stripe down the 2 controllers. For every volume group u create you use 2 LUNs. E.g. If you want 10GB, u would create lun 0 and lun 1 each at 5GB, an example ioscan would show you c5t2d0, c5t2d1, c6t3d0, c6t3d1. Create your vg using c5t2d0 & c6t3d1, vgextend it to include the alternate paths. When you create your logical volumes use:

lvcreate -i2 -I64 -L 10000 -n lveg /dev/vgeg

This tells it to stripe your logical volume across the 2 luns so it sends 64k chunks down each controller to your logical volume.

You can check it by doing an lvdisplay of the lv and it'll show you it striped across the 2 luns.

Of course you will need to backup your data first.

The AutoRAID takes the mgnt overhead from u and if setup correctly it can be very performant.

Hope this helps, Paul

[William Shaw]

Actually I've got an XP256, and if I assign a single LUN to 2 different ports connected to my HP server, I was wondering if anything on the host side would load balance between the 2 paths to that LUN. (in a SUN enviromnemt, for example, when VxVM [ie: LVM] detects 2 paths to the same target, load balancing is enabled by default. Apparently HP's version of VxVM doesn't do this).

[Dave Wherry]

I also have an XP256 and to answer your question, no, it does not automatically load balance. The alternate link is only used if the primary fails or the primary is removed from the volume group with a vgreduce command.
The way to load balance is to use extent based striping across your interfaces to different LUNs.
For example, each mount point/file system for my Oracle database uses 4 Open-8 LUNs. When I created the logical volumes I used the "-D y" option with a physical volume group which includes those 4 LUNs. The first extent is created on the first LUN on the first interface. The next extent on the next LUN and interface and so on, in a round robin style. I/O is then balanced very well across the 4 interfaces.

[Brenda McLaren]

The other way that you can load balance without striping is through the use of the PV links. Set the primary path to each disk in the volume group to an alternate controller. Do this by removing the primary path and then readding it. It may not be perfect, but it helps.

Brenda

[Anthony Goonetilleke]

There is also a great product from EMC called powerpath that does load balancing across alternate paths. Its is very effective and works quite well. Its is also dynamic so its not like you are dividing devices between paths and hoping for the best.

[David Child_1]

I just wanted to comment on the PowerPath product from EMC. PowerPath is a great product in that it does true load balancing. The striping methods that have been mentioned so far should work pretty good, but it isn't true load balancing (it's more of a load distribution). The PowerPath software dynamically sends data down various paths (up to 32) based on workload so no one path will get overloaded while another is idle. The only catch is that I believe it only works with EMC's Symmetrix Enterprise Storage Systems.

[Manju Kampli]

william,

You can use PVGs and Mirroring to get the load balancing and protect from single point failure.
Unfortunately the LVM does not provide the load balancing.

Create PVGs with disks from same controller and mirror them across to other PVG which is created on different controller. The disks in the PVGs will be stripped and also be mirroed using LVM.. If you use LVM stripping, you can not do mirroring.

so when you do write, it will be get written on both controllers and also all the disks ( since they are stripped)

I have been following this method and the performance and data protection is really working fine.

Hope this helps,
Manju

[Stefan Farrelly]

Powerpath is for EMC, not HP's XP256/512's. The equivalent is using Veritas Volume Manager (instead of LVM). This does load balancing across alternate links (pvlinks). Works great.

[Denver Osborn]

LVM doesn't provide load balancing, only fail over. On 11i with HP's release of VxVM it will do load balancing, but you have to install an addition product to get it. Product B9116AA. The 11i base VxVM won't do load balancing.

This information is available at http://www.docs.hp.com//hpux/onlinedocs/B7961-90017/00/00/11-con.html

Hope this helps!
-denver

[Tim D Fulford]

I thought HP-UX 11.i did load balancing?

Just a thought

Tim

[Bill McNAMARA_1]

lvm does not load balance (at least not until late 2002 I heard.) But the veritas volume manager for hpux11i does, once you buy a non default installation licence from veritas.

Later,
Bill

[Duncan Edmonstone]

If you have an XP256, and you want to load balance *properly*, rather than the clever methods discussed above, you should look at HP Surestore AutoPath XP, which is the HP equivalent of EMC's PowerPath product. See the following URL for more info...

http://www.hp.com/products1/storage/disk_arrays/infolibrary/auto_path.pdf

Cheers,

Duncan

[Tom Danzig]

I don't think AutoPath XP is for HP-UX (mainly for Windows).
The way we do it with our XP512 is to always use an even number of LDEV's to a volume group and use LVM striping when defining the lvols to balance the load accross controllers.