Hello Paolo, Before anyone expends any cycles on my last message, I have new information.
Today I was able to eliminate the file corruption issue by doing a 'blockdev --flushbufs' prior to taking a snapshot. I haven't done extensive testing yet, but it seems the issue if gone at this point. So sorry for the disruption. Best regards, Mark Trumpold On 10/22/12 8:10 AM, "Mark Trumpold" <ma...@netqa.com> wrote: >Paolo, > >Please recall you had sent me the link below to a kernel patch to allow >'qemu-nbd' to flush to disk. The patch was applied with good success. > >However, recent testing indicates that filesystem corruption issue I am >seeing seems to be tied to large (>500mbyte) filesystem writes. I also >observe the kernel 'flush' thread approaching 100% cpu at times, and i/o >wait % as reported by 'top' increasing sharply during the copy/write. > >Was wondering if perhaps there are any special kernel config options that >I may be missing for 'nbd', or any other information that might help. > >Best regards, >Mark Trumpold > > >>-----Original Message----- >>From: Paolo Bonzini [mailto:paolo.bonz...@gmail.com] On Behalf Of Paolo >>Bonzini >>Sent: Wednesday, September 12, 2012 11:30 PM >>To: Mark Trumpold >>Cc: qemu-devel@nongnu.org >>Subject: Re: 'qemu-nbd' explicite flush to disk >>Il 12/09/2012 23:28, Mark Trumpold ha scritto: >>> So, I've been experimenting with 'qemu-nbd --cache=writeback ..' >>> This nicely eliminates the 'checkpoint' issue; however, I have as >>> yet been unable to explicitely flush things to disk -- which I would >>>like to >>> do just before a 'nilfs' snapshot. > >>The Linux kernel driver for NBD does not support flushes. Patches were >>sent to the maintainer, but he never applied them. >>You can get them at >>http://thread.gmane.org/gmane.linux.drivers.nbd.general/1108 and try >>them. >>> Subsequently I've been trying to call 'bdrv_co_flush(bs)' directly, >>>but >>>I can't >>figure out how to dereference 'bs' for the call. >>> >>> I'm probably out in the weeds on this one. >>> Any guidance would be greatly appreciated. >>> >>> I am running: >>> qemu-1.2.0 >>> linux kernel 3.3.1 >>> >>> Thank you, >>> Mark Trumpold
