Hi Malahal, Thanks for your response.
On Wed, Jul 15, 2009 at 09:41:58AM -0700, mala...@us.ibm.com wrote: > > I've been playing with kvm (virtio_blk, writeback) -> dm_multipath > > (failover, queue_if_no_path) -> open-iscsi -> gigE -> IET on a new > > server, winding up the queue and segment lengths and I'm getting > > frequent disconnects during heavy writes from the KVM guest. Wireshark > > shows a PDU with a incorrect DataDigest (sample at > > http://www.interspeed.co.nz/crcerr.pcap for a little while) just before > > IET resets the connection (reasonably, if it gets the same CRC mis-match). > > What kind of application are you using to generate the write I/O? It is The application is KVM (qemu-kvm-0.10.5), running a single Debian Lenny instance with the iscsi device visible to the guest as a virtio disk. I've found running this on the guest is a pretty reliable way to produce the problem: find / > /dev/null ; sync The guest filesystems are ext3, so presumably journal flushes are the trigger ... > possible that a file system (or some other application) can modify the > write buffer once it is submitted to the block layer. Any modification > done after generating CRC is going cause CRC mismatch. This is a well > known problem! Do you mean a well known problem with zero-copy block devices or a well known problem with iscsi with data digests? I've been trawling through the code and if I understand correctly, iscsi_sw_tcp_xmit_segment() uses iscsi_tcp_segment_done() to calculate the digest after each sendpage or sendmsg. Do you think the segment data might be getting modified in between sendpage/sendmsg and packet assembly? (sendpage looks to be sock_no_sendpage if data digests are enabled.) If access to the segment data isn't exclusive during the execution of iscsi_sw_tcp_xmit_segment(), then I suppose there is also the chance the data might be altered between sendpage/sendmsg and crypto_hash_final() completing. (FWIW, the same thing happens with 871, built from source.) Thanks, Mark. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-iscsi@googlegroups.com To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/open-iscsi -~----------~----~----~----~------~----~------~--~---
