[linux-lvm] Where are the data blocks of an LV?

[linux-lvm] Where are the data blocks of an LV?

[Marcin Owsiany]

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Hello,

I know that it is possible to find where a given logical volume's extents
start on a PVs thanks to the information printed by lvdisplay --maps.

I was also able to experimentally establish that the actual data of an LV
starts one megabyte after that location. Is that offset documented
anywhere, or can I somehow discover it at runtime for a given LV?

regards,
Marcin

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Re: [linux-lvm] Where are the data blocks of an LV?

[Roger James]

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See https://talk.manageiq.org/t/lvm-internals-structures-disk-layout/1328

On 26 July 2022 09:16:31 Marcin Owsiany <marcin@owsiany.pl> wrote:
> Hello,
>
> I know that it is possible to find where a given logical volume's extents 
> start on a PVs thanks to the information printed by lvdisplay --maps.
>
> I was also able to experimentally establish that the actual data of an LV 
> starts one megabyte after that location. Is that offset documented 
> anywhere, or can I somehow discover it at runtime for a given LV?
>
> regards,
> Marcin
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://listman.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/


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Re: [linux-lvm] Where are the data blocks of an LV?

[Stuart D Gathman]

Checkout https://github.com/sdgathman/lbatofile
It was written to identify the file affected by a bad block (so it goes
the opposite direction), but the getpvmap() function obtains pe_start and 
pe_size plus the list of segments.  findlv() goes through the segments to
find the one an absolute sector is in.  That should tell you what you want 
to know.

On Fri, 22 Jul 2022, Marcin Owsiany wrote:

> I know that it is possible to find where a given logical volume's extents
> start on a PVs thanks to the information printed by lvdisplay --maps.
> 
> I was also able to experimentally establish that the actual data of an LV
> starts one megabyte after that location. Is that offset documented anywhere,
> or can I somehow discover it at runtime for a given LV?

_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/