/var/log/messages的錯誤描述
Sep 14 04:02:58 kernel: connection4:0: detected conn error (1011)
Sep 14 04:02:59 iscsid: Kernel reported iSCSI connection 4:0 error (1011) state (3)
Sep 14 04:03:01 kernel: connection3:0: detected conn error (1011)
Sep 14 04:03:02 iscsid: Kernel reported iSCSI connection 3:0 error (1011) state (3)
Sep 14 04:03:02 kernel: connection1:0: detected conn error (1011)
Sep 14 04:03:02 kernel: connection8:0: detected conn error (1011)
Sep 14 04:03:02 kernel: connection2:0: detected conn error (1011)
Sep 14 04:03:02 kernel: connection5:0: detected conn error (1011)
Sep 14 04:03:03 iscsid: Kernel reported iSCSI connection 1:0 error (1011) state (3)
Sep 14 04:03:03 iscsid: Kernel reported iSCSI connection 8:0 error (1011) state (3)
Sep 14 04:03:03 iscsid: Kernel reported iSCSI connection 2:0 error (1011) state (3)
Sep 14 04:03:03 iscsid: Kernel reported iSCSI connection 5:0 error (1011) state (3)
Sep 14 04:03:04 iscsid: connection4:0 is operational after recovery (1 attempts)
Sep 14 04:03:08 iscsid: connection3:0 is operational after recovery (1 attempts)
Sep 14 04:03:08 iscsid: connection8:0 is operational after recovery (1 attempts)
Sep 14 04:03:08 iscsid: connection2:0 is operational after recovery (1 attempts)
Sep 14 04:03:08 iscsid: connection1:0 is operational after recovery (1 attempts)
Sep 14 04:03:08 iscsid: connection5:0 is operational after recovery (1 attempts)
解決方法：
用lsscsi命令查看錯誤的connection對應的disk （/dev/sdX）
[0:0:0:0] cd/dvd Optiarc DVD-ROM DDU820S MH52 /dev/scd0
[2:0:0:0] disk LEFTHAND iSCSIDisk 9500 /dev/sdj
[3:0:0:0] disk LEFTHAND iSCSIDisk 9500 /dev/sdk
再去iscsi存儲查看每個volume的iscsi session
發現有問題的volume對應的iscsi session有兩個或者在兩個中間切換，說明有多於一個session嘗試登入。
幸運的是，另一個session只是login，沒有掛載，不然就有可能破壞這個disk。
找到另外那個session對應的服務器，登出iscsi，問題解決。