[linux-lvm] some questions

Christoph Anton Mitterer calestyo at scientia.net
Thu Jul 18 18:43:00 UTC 2013


Hi.

I'd have some questions...

1) Is the --discards option the same than the issue_discards option from
the config file? Since the one defaults to 0 the other to passdown?
If not what's the difference?


2) Of an existing LV, can I see how data was actually allocated? And how
can I see the alloc policy of a VG? vgdisplay doesn't show it.


3) Do I see that correctly, when I use Normal as alloc policy,... it
will try to do contiguous allocation... and only do not so,... if not
possible?


4) md_component_detection and md_chunk_alignment
Will these also work if there is another block layer (e.g. dmcrypt) in
between? Especially the md_chunk_alignment?


5) What alignments are needed?
"md_chunk_alignment — If set to 1, and a Physical Volume is placed
directly upon an md device, LVM2 will align its data blocks with the md
device's stripe-width."

Implies that something needs to be aligned to the strip width (I guess
you mean the chunk_size * number_of_data_chunks (i.e. not counting
parity)?)?
What is that? Should the PEs be aligned to the stripe width? I.e.
multiple PEs exactly in one stripe, or multiple stripes exactly in one
PE?


Thanks,
Chris.
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