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

[Jonathan Buzzard]

Doing an upgrade on our storage which involved replacing all the 4TB 
disks with 16TB disks. Some hiccups with five of the disks being dead 
when inserted but that is all sorted.

So the system was originally installed with DSS-G 2.0a so with "legacy" 
commands for vdisks etc. We had 10 metadata NSD's and 10 data NSD's per 
draw aka recovery group of the D3284 enclosures.

The dssgmkfs.mmvdisk has created exactly one data and one metadata NSD 
per draw of a DS3284 leading to a really small number of NSD's in the 
file system.

All my instincts tell me that this is going to lead to horrible 
performance on the file system. Historically you wanted a reasonable 
number of NSD's in a system for decent performance.

Taking what the ddsgmkfs.mmvdisk has give me even with a DSS-G260 you 
would get only 12 NSD's of each type, which for a potentially ~5PB file 
system seems on the really low side to me.

Is there any way to tell ddsgmkfs.mmvdisk to create more NSD's than the 
one per recovery group or is this no longer relevant and performance 
with really low numbers of NSD's is fine these days?


JAB.

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