LVM and VxVM

Parallel Read operations with mirror disk

 
christoph ernst_4
Occasional Visitor

Parallel Read operations with mirror disk

Hi LVM experts!

 

Hi have a rx6600 with 6 disks for a oracle database.

 

The LVs of the oracle db are striped on three disks and then mirrored on the other three disks. I would expect the same i/o load on all six disks when i measure it with sar because of parallel read/write operations. But the i/o load is different. It seems HP-UX does not do parallel read operations on the mirrored disks, right? Is it configurable that HP-UX will balance the read operations on both sides of the mirror?

 

In the attachement you can find the lvm config and the sar output.

3 REPLIES 3
Torsten.
Acclaimed Contributor

Re: Parallel Read operations with mirror disk

Are all disks same size and speed?


Hope this helps!
Regards
Torsten.

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christoph ernst_4
Occasional Visitor

Re: Parallel Read operations with mirror disk

Yes, all six disks are identical models.

Bill Hassell
Honored Contributor

Re: Parallel Read operations with mirror disk

The normal operation is to read only from the first or primary disk, but write in parallel to both disks. It makes no sense to read for disks at the same time since the data is the same. If you are expecting the reads to alternate between the two disks, this would get very complicated to when the reads are smaller or larger than the extent sizes. I'm not aware of any path managers that will load balance between mirrors since mirrors are an LVM concept. Load balancing is done by path managers for alternate paths to the same disk.



Bill Hassell, sysadmin