--Angelo
Dave B wrote:
This is still causing me headaches... Does anybody have any insight on this?
--- bowmailtmp-lvm@yahoo.com wrote:
ok, i think i've got an idea what's going on here,
it
seems that the lvm cache may be the problem here. it
seems like in some cases if i wait a couple
*minutes*
then the data magically shows up in the proper
physical sectors of the disk. in some cases it is
faster, some quite slow. can someone confirm this
for
me and give me an idea of the mechanics involved
with
the cache? also, is there a command to force the
cache to be flushed out? i'll keep looking through
the man pages for this.
thanks, dave
--- bowmailtmp-lvm@yahoo.com wrote:
I have been having a very difficult time
correlating
physical addresses to LVM2/DM addresses.
for instance, if i do: dmsetup table /dev/mapper/avtest-vdisk2g
the result is: 0 4194304 linear 22:65 384
from what i currently understand, this means
logical
extent 0 (which is composed of 8192 512 byte
sectors
in the default config) of this LV should start at physical sector 384 of device 22:65 (/dev/hdd1 on
my
machine)
after i've written to the logical device a couple times, it appears this correlation doesn't hold
when
i
access the physical sectors on hdd1 using dd. however, if i use dd to access the sectors through
the
LV, all the data appears as it should. i was
under
the impression that the logical to physical
mappings
was quite straightforward and intuitive, but i
feel
that i am missing some key information. Can
someone
help me out of is there decent developer documentation somewhere that explains the mappings?
As a more complete example of my problem, if i do the following:
dd if=/dev/zero of=/dev/avtest/vdisk2g count=1 then do: dd if=/dev/avtest/vdisk2g of=tmpfile.out count=1 then tmpfile.out contains 512 bytes of zeros.
however, if I do: dd if=/dev/hdd1 of=tmpfile.out skip=384 count=1 then tmpfile.out contains other data, not the
zero's
i would expect from the output of the dmsetup table command above. I feel i'm missing something
fairly
basic here, but I haven't had any luck tracking
this
relationship down. I suppose there is always the sourc code :)
Thanks a lot.
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