> not sure it's related, but with O_DIRECT I think that the write need to be aligned with multiple of 4k block. (or 512bytes) That is right and you just can't use O_DIRECT without alignment. You would just get an error on "write" system call. If you check drbd_oos_test.c you find posix_memalign there.
On Thu, May 28, 2015 at 10:33 AM, Alexandre DERUMIER <aderum...@odiso.com> wrote: > Hi, > > not sure it's related, but with O_DIRECT I think that the write need to be > aligned with multiple of 4k block. (or 512bytes) > > (and I remember some bug with qemu and and 512b-logical/4k-physical disks > > http://pve.proxmox.com/pipermail/pve-devel/2012-November/004530.html > > I'm not an expert so I can't confirm. > > ----- Mail original ----- > De: "Stanislav German-Evtushenko" <ginerm...@gmail.com> > À: "dietmar" <diet...@proxmox.com> > Cc: "aderumier" <aderum...@odiso.com>, "pve-devel" < > pve-devel@pve.proxmox.com> > Envoyé: Jeudi 28 Mai 2015 09:22:12 > Objet: Re: [pve-devel] Default cache mode for VM hard drives > > Hi Dietmar, > > I did it couple of times already and everytime I had the same answer > "upper layer problem". Well, as we've done this long way up to this point I > would like to continue. > > I have just done the same test with mdadm and not DRBD. And what I found > that this problem was reproducible on the software raid too, just as it was > claimed by Lars Ellenberg. It means that problem is not only related to > DRBD but to O_DIRECT mode generally when we don't use host cache and a > block device reads data directly from userspace. > > The testcase is bellow. > > 1. Prepare > > dd if=/dev/zero of=/tmp/mdadm1 bs=1M count=100 > dd if=/dev/zero of=/tmp/mdadm2 bs=1M count=100 > losetup /dev/loop1 /tmp/mdadm1 > losetup /dev/loop2 /tmp/mdadm2 > mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/loop{1,2} > > 2. Write data with O_DIRECT > > ./a.out /dev/md0 > > 3. Check consistency with vbindiff > > vbindiff /tmp/mdadm{1,2} #press enter multiple times to skip metadata > > And here we find that data on "physical devices" is different and md raid > did not catch this. > > > On Thu, May 28, 2015 at 7:40 AM, Dietmar Maurer < diet...@proxmox.com > > wrote: > > > > What this means? > > I still think you should discuss that on the DRBD list. > > > > > > Best regards, > Stanislav German-Evtushenko >
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