in a previous post yuri did explain how GPFS determines the order in which it stripes writes to disks. I wonder whether I can change this order after the initial storage pool creation? I want to do this for two reasons:
- I did the intital ordering wrong, I didn't alternate controllers as recommended by yuri
- I want to add more controllers and luns to an existing storage pool, hence I want to reorder the stripe-sequence, otherwise all new LUNs will be added as one block.
If I need to shutdown all nodes and say, edit the mmsdrfs file, that would be o.k.. I do run gpfs 3.5.0-13 on linux.
Citation from previous post by yuri:
The NSD stripe ordering is controlled entirely by the order of NSDs, something that's specified by the disk descriptor file given to mmcrfs/mmadddisk, and can be queried via mmlsdisk. If the latter lists, say "nsd1; nsd2; nsd3; nsd4", that's going to be the disk order for striping.
In order to spread the IO across multiple arrays, one has to be judicious about the order in which disks are listed in the original disk descriptor at mmcrfs/mmadddisk time. Instead of doing "disk1-from-controller1; disk2-from-controller1; ...; disk1-from-controller2; disk2-from-controller2" one should choose "disk1-from-controller1; disk1-from-controller2; ...; disk2-from-controller1; disk2-from-controller2".