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LVM over raid : extent size calculation

Hello to all, 

I'm going to do some playing (and heavy testing) with LVM over MD raid.
I want to try abusing several types of arrays with several types of file
systems so I have data handy should I ever need to use it.

I want to see which types of FS's are likely to fail in this setting
under heavy abuse circumstances such as intentionally flooding inodes,
unclean reboots.. as far as I can go without actually risking hardware
itself. I also want to test a few types of cluster file systems (namely

My question is , what is the correct way to calculate the physical
extent size of a volume group relative to the size of the array?

Obviously the physical extent size is going to have to be (much) greater
than the default for large arrays.

For instance, lets say /dev/md4 has been setup as raid5 and totals ...
800 GB. How would I determine the physical extent size to pass to
vgcreate? Am I going to run into issues over-sizing it?

Is there a mb per GB of space in the array ratio to follow, or some
other way to calculate this?

Many thanks in advance!


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