Hello all,
I tried a simple test:
1. Installed an iSCSI target. I tried this with both IET
(iscsitarget.sourceforge.net) and tgt (apt-get install tgt).
2. Created a 2GB file to use as the target.
3. Connected to the target with iscsiadm.
4. Ran the following command to test read throughput: dd if=/dev/sdc
of=/dev/null bs=128M count=16
5. Ran the following command to test write throughput: dd if=/dev/zero
of=/dev/sdc bs=128M count=16
(where /dev/sdc is the iSCSI device)
For read throughput I get about 98MB/s, and for write throughput about
75MB/s. I tried to figure out why writes are so much slower, so I
opened up wireshark and looked at the packets. I captured 256,270
packets. Here are some statistics from wireshark:
Bad checksum(TCP): 35,963
Bad checksum(UDP): 4
Previous segment lost (TCP): 24,502
ACKed lost segment (TCP): 51,651
I would bet that this has something to do with the low throughput.
(For the read test, everything looks fine in wireshark). I uploaded
the compressed dump here:
http://www.fsl.cs.sunysb.edu/~avishay/iscsi-loopback-write.dump.tgz
I'm assuming the problem lies in open-iscsi because I tried two
different targets with the same results, and I'm working over loopback
(no network issues).
Some more info:
# uname -a
Linux guri 2.6.24-16-server #1 SMP Thu Apr 10 13:15:38 UTC 2008 x86_64
GNU/Linux
# cat /etc/issue
Ubuntu 8.04.1 \n \l
# iscsiadm -V
iscsiadm version 2.0-865
# dpkg -l | grep open-iscsi
ii open-iscsi
2.0.865-1ubuntu3 High performance, transport
independent iSCS
# iscsiadm -m discovery -t st -p 127.0.0.1
127.0.0.1:3260,1 iqn.2001-04.com.example:storage.disk2.sys1.xyz
# iscsiadm -m node -T iqn.2001-04.com.example:storage.disk2.sys1.xyz -
p 127.0.0.1 -l
Login session [iface: default, target: iqn.
2001-04.com.example:storage.disk2.sys1.xyz, portal: 127.0.0.1,3260]
# fdisk -l /dev/sdc
Disk /dev/sdc: 2147 MB, 2147483648 bytes
67 heads, 62 sectors/track, 1009 cylinders
Units = cylinders of 4154 * 512 = 2126848 bytes
Disk identifier: 0x
Disk /dev/sdc doesn't contain a valid partition table
Any help would be appreciated!
Thanks a lot!
Avishay
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