From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with ESMTP id i6DNco001816 for ; Tue, 13 Jul 2004 19:38:50 -0400 Received: from web11808.mail.yahoo.com (web11808.mail.yahoo.com [216.136.172.162]) by mx3.redhat.com (8.12.10/8.12.10) with SMTP id i6DNchXn022626 for ; Tue, 13 Jul 2004 19:38:44 -0400 Message-ID: <20040713233843.7906.qmail@web11808.mail.yahoo.com> Date: Tue, 13 Jul 2004 16:38:43 -0700 (PDT) From: Subject: Re: [linux-lvm] LVM2/DM Mapping Tables Documentation In-Reply-To: <20040713212312.81503.qmail@web11803.mail.yahoo.com> MIME-Version: 1.0 Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: LVM general discussion and development 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/ >