higher agcount on LVM2 thinp volumes

[Stan Hoeppner]

On 8/29/2013 1:09 AM, Chris Murphy wrote:
> 
> Is it expected when formatting, using defaults, that a thinp volume compared to either a conventional LV or partition of the same size, should have a higher agcount?
> 
> 
> HDD, GPT partitioned, 100GB partition size:
> 
> [root at f19s ~]# mkfs.xfs /dev/sda7
> meta-data=/dev/sda7              isize=256    agcount=4, agsize=6553600 blks
>          =                       sectsz=512   attr=2, projid32bit=0
> data     =                       bsize=4096   blocks=26214400, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0
> log      =internal log           bsize=4096   blocks=12800, version=2
>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> 
> 
> A 400GB partition, made into PV, PV added to VG, and all extents put into a thinpool volume, a 100GB virtual sized LV:
> 
> [root at f19s ~]# mkfs.xfs /dev/mapper/vg1-data
> meta-data=/dev/mapper/vg1-data   isize=256    agcount=16, agsize=1638400 blks
>          =                       sectsz=512   attr=2, projid32bit=0
> data     =                       bsize=4096   blocks=26214400, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0
> log      =internal log           bsize=4096   blocks=12800, version=2
>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> 
> 
> 
> I get agcount=4 on a conventional LV as well. Why agcount=16 on thinp?

More information would be helpful, specifically WRT the device stack
underlying mkfs.xfs.  I.e. we need to know more about the LVM configuration.

See:

http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F

-- 
Stan