topic Re: Load Balancing under HP-UX in Operating System - HP-UX

Load Balancing under HP-UX

Carl T. Fulp — Mon, 16 Oct 2000 11:17:24 GMT

I define load balancing as the distribution of I/O requests across multiple channel paths to a device. Does LVM under HP-UX provide load balancing or is additional software such as Veritas Volume Manager required. Is the alternate path of a disk device under LVM used just for failover or is it also used when the primary path is busy (load balancing)?

Thanks

Re: Load Balancing under HP-UX

Andreas Voss — Mon, 16 Oct 2000 11:24:33 GMT

Hi,

if you have devices with alternate links (ie: AutoRaid) you can control balancing at volume group creation time (vgcreate/vgextend).
Example:
Controller X: /dev/dsk/c1t0d0
Controller Y: /dev/dev/c3t0d0
Add one vg:
vgcreate vg01 /dev/dsk/c1t0d0
vgextend vg01 /dev/dsk/c3t0d0
This will result in vg01 has primary /dev/dsk/c1t0d0 and alternate /dev/dsk/c3t0d0
Add another vg:
vgcreate vg02 /dev/dsk/c3t0d0
vgextend vg02 /dev/dsk/c1t0d0
This will result in vg02 has primary /dev/dsk/c3t0d0 and alternate /dev/dsk/c1t0d0

So you can control I/O-balancing with the order of the device files when doing vgcreate/vgextend.

Regards

Re: Load Balancing under HP-UX

John Palmer — Mon, 16 Oct 2000 11:30:05 GMT

Hi,

The alternative path is only used for failover.

Regards,
John

Re: Load Balancing under HP-UX

Andy Monks — Mon, 16 Oct 2000 11:37:26 GMT

If your using lvm mirroring, it does try and balance read accesses based upon shorted i/o queue. Obviously writes have to occur to all mirror copies.

However as the others have said, lvm will only use the alternate path should the primary fail.

Therefore you can help the system but alternating which path is the primary and alternate.

Re: Load Balancing under HP-UX

Andreas Voss — Mon, 16 Oct 2000 11:41:18 GMT

Hi (again),

if you have multiple disks within one vg you can use striping (and also mirroring = distributed striping+mirroring) to have I/O balancing.
Manually you can use the pvmove command for distributing the extends to different disks of the log. volumes.

Regards

Re: Load Balancing under HP-UX

Rita C Workman — Mon, 16 Oct 2000 12:00:51 GMT

I have to agree with what has already been stated.

But I will throw this one out there. We have an EMC Disk Array, and have found that EMC offers a utility called, I believe, 'PowerPath'. What this does is allow the alternate link to become a second i/o channel for normal production. Basically it doubles i/o.
I know we're getting it on some new hardware coming in...and boy do I wish I had it currently on the production running today. ..sigh...

The point is - here is one vendor who has this type of service. So maybe you could check and see if your vendors have something comparable.

Re: Load Balancing under HP-UX

Carl T. Fulp — Mon, 16 Oct 2000 14:00:51 GMT

Thanks for all the replies. In summary, based on the replies, I believe the answer is that LVM doesn't provide load balancing by default. Though you can alter the configuration definition to obtain an a step toward load-balancing; a third-party product is required for true load-balancing.

Thanks.