[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: [linux-lvm] LVM2/DM Mapping Tables Documentation



I believe the command "sync" at a shell prompt will flush the cache to disk. Someone correct me if I'm wrong.

--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.




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


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



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

Attachment: signature.asc
Description: OpenPGP digital signature


[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]