Re: [gpfsug-discuss] Clarification about blocksize in stardanrd gpfs and GNR

Thu, 21 Mar 2019 10:15:53 -0700

Alvise,
 
Also note that that DeveloperWorks page was maintained by Scott Faddon. He has since left IBM and that page has unfortunately not been updated for almost 2 years. :-(
 
This page predates the current version 5.x of SpectrumScale which has been available since the beginning of 2018.
 
In version 5.x. the statement that there are 32 sub-blocks in one block is no longer true.
Now, by default you get a 4MiB Filesystem blocksize that has 512 sub0clocks, each 8192 bytes long.
Daniel
 
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Daniel Kidger
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Spectrum Scale, Spectrum NAS and IBM Cloud Object Store

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----- Original message -----
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Subject: Re: [gpfsug-discuss] Clarification about blocksize in stardanrd gpfs and GNR
Date: Thu, Mar 21, 2019 1:32 PM
 
The underlying device in this context is the NSD, network storage device. This has relation at all to 512 byte or 4K disk blocks. Usually around a meg, always a power of two. 
 
  -- ddj
Dave Johnson

On Mar 21, 2019, at 9:22 AM, Dorigo Alvise (PSI) <[email protected]> wrote:
 
Hi,
I'm a little bit puzzled about different meanings of blocksize for different GPFS installation (standard and gnr).
 
 
I read:
  • The blocksize is the largest size IO that GPFS can issue to the underlying device
  • A subblock is 1/32nd of blocksize. This is the smallest allocation to a single file
For non-gnr GPFS device is quite clear to me (I hope): it is a single spinning disk (or ssd). And I verified this on a small cluster composed of nsd using their local hard drive.
 
Can someone explain what is the "device" in the case of GNR ? a single pdisk ?
 
Thanks,
 
  Alvise
 
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