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The server has been running iSCSI service for the diskless client, and I have noticed that the connection of server's gateway(internet connection or a fake gateway) made iSCSI performance worse.
Is there anybody who has experienced this OR who could give any suggestion for debugging?

FYI: the results of 'fio' test are OK even if the default gateway is connected. So I think that the issues are in iSCSI.

Environment:
  CentOS 7.7.1908 / Kernel 3.10.0-1062.18.1.el7.x86_64
  ZFS version zfs-0.8.3-1 / zfs-kmod-0.8.3-1
  targetcli version 2.1.fb46
  Server NIC: Intel 4 ports 1Gbps, 4 ports trunk
  Switch: 1Gbps 48 ports, 4 ports trunk

zpool iostat when server's default gateway is connected. (attached cable)
              capacity     operations     bandwidth
pool        alloc   free   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
zp1          177G   751G    470     85  56.8M  8.82M
zp1          177G   751G    684     34  83.4M  3.12M
zp1          177G   751G    414    979  49.6M  90.7M

zpool iostat when server's default gateway is not connected. (detached cable)

              capacity     operations     bandwidth
pool        alloc   free   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
zp1          176G   752G  2.19K    445   276M  3.45M
zp1          176G   752G  2.50K    428   314M  4.21M
zp1          176G   752G  1.92K      3   243M  60.0K
sohnman
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  • You should always run iSCSI on a dedicated NIC and preferrably on a dedicated, separated, unrouted subnet & VLAN. – Zac67 Dec 18 '20 at 12:55
  • @Zac67 At first, thank you for the comment and I'll separate it by VLAN. FYI, Replacing 100Mbps gateway with 1Gbps gateway makes bandwidth of 'zpool iostat' better like case as the detached cable. I don't know why... ^^; – sohnman Dec 20 '20 at 11:42
  • I can try checking how network traffic goes in both configurations to identify what's your bottleneck. Wireshark or alternatives can be used. – Stuka Dec 20 '20 at 17:01

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