[gpfsug-discuss] Initial file placement

[Buterbaugh, Kevin L]

Hi yet again all,

Well, this has turned out to be an enlightening and surprising morning in GPFS land…

What prompted my question below is this … I am looking to use the new QoS features in GPFS 4.2.  I have QoS enabled and am trying to get a baseline of IOPs so that I can determine how much I want to assign to the maintenance class (currently both maintenance and other are set to unlimited).  To do this, I fired off a bonnie++ test from each of my NSD servers.

The filesystem in question has two storage pools, the system pool and the capacity pool.  The system pool is comprised of a couple of metadata only disks (SSD-based RAID 1 mirrors) and several data only disks (spinning HD-based RAID 6), while the capacity pool is comprised exclusively of data only disks (RAID 6).

When the bonnie++’s were creating, reading, and rewriting the big file they create I was quite surprised to see mmlsqos show higher IOP’s on the capacity pool than the system pool by a factor of 10!  As I was expecting those files to be being written to the system pool, this was quite surprising to me.  Once I found the mmlsattr command, I ran it on one of the files being created and saw that it was indeed assigned to the capacity pool.  The bonnie++’s finished before I could check the other files.

I don’t have any file placement policies in effect for this filesystem, only file migration policies (each weekend any files in the system pool with an atime > 60 days get moved to the capacity pool and any files in the capacity pool with an atime < 60 days get moved to the system pool).

In the GPFS 4.2 Advanced Administration Guide, it states, “If a GPFS file system does not have a placement policy installed, all the data is stored in the first data storage pool.”

This filesystem was initially created in 2010 and at that time consisted only of the system pool.  The capacity pool was not created until some years (2014?  2015?  don’t remember for sure) later.  I was under the obviously mistaken impression that the “first” data storage pool was the system pool, but that is clearly not correct.

So my first question is, what is the definition of “the first storage pool?” and my second question is, can the documentation be updated with the answer to my first question since it’s clearly ambiguous as written now?  Thanks…

Kevin

On Jun 17, 2016, at 9:29 AM, Buterbaugh, Kevin L <Kevin.Buterbaugh at Vanderbilt.Edu<mailto:Kevin.Buterbaugh at vanderbilt.edu>> wrote:

Hi All,

I am aware that with the mmfileid command I can determine which files have blocks on a given NSD.  But is there a way to query a particular file to see which NSD(s) is has blocks on?  Thanks in advance…

Kevin

—
Kevin Buterbaugh - Senior System Administrator
Vanderbilt University - Advanced Computing Center for Research and Education
Kevin.Buterbaugh at vanderbilt.edu<mailto:Kevin.Buterbaugh at vanderbilt.edu> - (615)875-9633



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—
Kevin Buterbaugh - Senior System Administrator
Vanderbilt University - Advanced Computing Center for Research and Education
Kevin.Buterbaugh at vanderbilt.edu<mailto:Kevin.Buterbaugh at vanderbilt.edu> - (615)875-9633



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