[linux-lvm] RAID and LVM?

Paul Jakma paul at clubi.ie
Tue Aug 3 20:24:46 UTC 1999

On Mon, 26 Jul 1999, David Venus wrote:
  I am guessing the difference is that one accesses the
  drive/device in block mode (bh_dev) and the other as a
  character/raw device (bh_rdev).

i'm not much of a kernel hacker, but i think b_dev/r_dev is
device/real device... ie md0/sda3 type of thing. but i'm not sure.

what i'd like to know is: if i'm right, why does lvm want to make
bh->b_dev=bh->b_rdev?? .. i don't know. it means if lvm tries to read
from mdx, then the md code is invoked with hd<something> instead of
md.. which fails miserably of course...

i left this hack out, and the kernel booted. RAID worked, LVM worked
on normal devices.. but the LVM tools gave errors when i tried to
build VLM ontop of a RAID device (ingo's latest raid that is).
The reason for the device remap is something to do with the original
md code, but i don't know why. Ingo's new RAID code should be pretty
transparent and hence LVM shouldn't need to do low-level fiddling
around in ll_rw_blk. an mdx device is afaik pretty much the same as
an hdax device.. (right?)

Paul Jakma
paul at clubi.ie	http://hibernia.clubi.ie
PGP5 key: http://www.clubi.ie/jakma/publickey.txt
Now and then an innocent man is sent to the legislature.

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