[linux-lvm] raid & its stripes

lejeczek peljasz at yahoo.co.uk
Wed Sep 13 13:53:58 UTC 2017

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

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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