[linux-lvm] raid & its stripes

[Brassow Jonathan]

Seems strange on the surface.  Would you mind posting the layout of each?  ‘lvs -a -o +devices’

 brassow

> On Sep 13, 2017, at 8:53 AM, lejeczek <peljasz at yahoo.co.uk> wrote:
> 
> hi boys, girls
> 
> man page reads: -i ...This is equal to the number of physical volumes to scatter the  logical  volume data....
> I wonder, when I do not use -i while creating an LV with 10 phy devs.
> 
> $ lvcreate -n raid0.A --type raid0 -I 16 -l 97%pv
> 
> a dbench would show:
> $ dbench -t 60 20
> ...
> Throughput 112.309 MB/sec  20 clients  20 procs  max_latency=719.409 ms
> 
> Yet when I say: this many stripes:
> 
> $ lvcreate -n raid0.A --type raid0 -I 16 -i 10 -l 97%pv
> 
> dbench:
> ...
> Throughput 83.2822 MB/sec  20 clients  20 procs  max_latency=816.027 ms
> 
> And though the results would vary, xfs, a dbench for LV with no -i as an argument(which LVM chooses then to be 2) would always look better.
> And I thought, as in the manual, always make stripes to go to all phy devices.
> 
> Question - is there some "little" magic LVM does? And if yes then how/what it is?
> many thanks, L.
> 
> .
> 
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