Thanks for your reply! yeah, i've tried this and it does do the trick for physical data queued up in the block device interface, but since LVM/DM provides an extra level of abstraction running sync at prompt, or even embedding fsync() into the C code after writes apparently has little to no effect on LVM volumes. I actually waited a couple HOURS the other day for data on a LV to actually show up in the promised sectors of the physical disk. -dave --- Angelo DiNardi <adinardi@slshs.org> wrote: > 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 part 1.2 application/pgp-signature name=signature.asc > _______________________________________________ > 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/
