[gpfsug-discuss] Blocksize

[Yuri L Volobuev]

The current (V4.2+) levels of code support bigger directory block sizes, so
it's no longer an issue with something like 1M metadata block size.  In
fact, there isn't a whole lot of difference between 256K and 1M metadata
block sizes, either would work fine.  There isn't really a downside in
selecting a different block size for metadata though.

Inode size (mmcrfs -i option) is orthogonal to the metadata block size
selection.  We do strongly recommend using 4K inodes to anyone.  There's
the obvious downside of needing more metadata storage for inodes, but the
advantages are significant.
yuri



From:	Jan-Frode Myklebust <janfrode at tanso.net>
To:	gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>,
Date:	09/22/2016 12:25 PM
Subject:	Re: [gpfsug-discuss] Blocksize
Sent by:	gpfsug-discuss-bounces at spectrumscale.org



https://www.ibm.com/developerworks/community/forums/html/topic?id=77777777-0000-0000-0000-000014774266

"Use 256K. Anything smaller makes allocation blocks for the inode file
inefficient. Anything larger wastes space for directories. These are the
two largest consumers of metadata space." --dlmcnabb

A bit old, but I would assume it still applies.


  -jf


On Thu, Sep 22, 2016 at 8:36 PM, Stef Coene <stef.coene at docum.org> wrote:
  Hi,

  Is it needed to specify a different blocksize for the system pool that
  holds the metadata?

  IBM recommends a 1 MB blocksize for the file system.
  But I wonder a smaller blocksize (256 KB or so) for metadata is a good
  idea or not...


  Stef
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