[gpfsug-discuss] dssgmkfs.mmvdisk number of NSD's

[Jonathan Buzzard]

On 28/02/2021 09:31, Jan-Frode Myklebust wrote:
> 
> I’ve tried benchmarking many vs. few vdisks per RG, and never could see 
> any performance difference.

That's encouraging.

> 
> Usually we create 1 vdisk per enclosure per RG,   thinking this will 
> allow us to grow with same size vdisks when adding additional enclosures 
> in the future.
> 
> Don’t think mmvdisk can be told to create multiple vdisks per RG 
> directly, so you have to manually create multiple vdisk sets each with 
> the apropriate size.
> 

Thing is back in the day so GPFS v2.x/v3.x there where strict warnings 
that you needed a minimum of six NSD's for optimal performance. I have 
sat in presentations where IBM employees have said so. What we where 
told back then is that GPFS needs a minimum number of NSD's in order to 
be able to spread the I/O's out. So if an NSD is being pounded for reads 
and a write comes in it. can direct it to a less busy NSD.

Now I can imagine that in a ESS/DSS-G that as it's being scattered to 
the winds under the hood this is no longer relevant. But some notes to 
the effect for us old timers would be nice if that is the case to put 
our minds to rest.


JAB.

-- 
Jonathan A. Buzzard                         Tel: +44141-5483420
HPC System Administrator, ARCHIE-WeSt.
University of Strathclyde, John Anderson Building, Glasgow. G4 0NG