Hi All,

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).

I can fiddle with various settings, but it basically seems that any 
tuning for performance triggers the error.  (Another possibly-relevant 
fact is that this shiny new server, came with a faster CPU and much more 
RAM than
two other servers with the same soft configuration, that do not show the 
problem).

iscsi_session/session105/abort_tmo: 15
iscsi_session/session105/data_pdu_in_order: 1
iscsi_session/session105/data_seq_in_order: 1
iscsi_session/session105/erl: 0
iscsi_session/session105/fast_abort: 1
iscsi_session/session105/first_burst_len: 65536
iscsi_session/session105/immediate_data: 1
iscsi_session/session105/initial_r2t: 0
iscsi_session/session105/lu_reset_tmo: 20
iscsi_session/session105/max_burst_len: 65536
iscsi_session/session105/max_outstanding_r2t: 1
iscsi_session/session105/recovery_tmo: 5
iscsi_session/session105/state: LOGGED_IN
iscsi_session/session105/tpgt: 1
iscsi_connection/connection105:0/address: 10.3.2.4
iscsi_connection/connection105:0/data_digest: 1
iscsi_connection/connection105:0/exp_statsn: 67
iscsi_connection/connection105:0/header_digest: 1
iscsi_connection/connection105:0/max_recv_dlength: 131072
iscsi_connection/connection105:0/max_xmit_dlength: 8192
iscsi_connection/connection105:0/persistent_address: 10.3.2.4
iscsi_connection/connection105:0/persistent_port: 3260
iscsi_connection/connection105:0/ping_tmo: 5
iscsi_connection/connection105:0/port: 3260
iscsi_connection/connection105:0/recv_tmo: 5

Everything is Debian Lenny, so iscsitarget 0.4.16+svn162-1 and 
open-iscsi 2.0.870~rc3-0.4.

Any ideas?  It seems plausible that it's an crc32c bug, but it could 
also be a collection error so I'm slightly nervous about just turning 
off data digests ...

Thanks,

Mark.

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