[gpfsug-discuss] Sub-block size wrong on GPFS 5 filesystem?

[Carl Zetie]

Kevin asks:
>>>>
Sorry  for the 2nd e-mail but I realize that 4 MB is 4 times 1 MB ? so does  this go back to what Marc is saying that there?s really only one sub  blocks per block parameter?  If so, is there any way to get what I want  as described below?
<<<

Yep. Basically what's happening is: 

When you ask for a certain block size, Scale infers the subblock size as shown in the table. As Sven said, here you are asking for 1M blocks for metadata, so you get 8KiB subblocks. So far so good.

These two numbers together determine the number of subblocks per block parameter, which as Marc said is shared across all the pools. So in order for your 4M data blocks to have the same number of subblocks per block as your 1M metadata blocks, the subblocks have to be 4 times as big. 

Something similar would happen with *any* choice of data block size above 1M, of course. The smallest size wins, and the 8KiB number is coming from the 1M, not the 4M. (Thanks, Sven).

regards,

 
Carl Zetie  
Offering Manager for Spectrum Scale, IBM  
----  
(540) 882 9353 ][ Research Triangle Park
 carlz at us.ibm.com