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Windows 2008 Web Edition and open source iSCSI targets

As I have mentioned in previous article on iscsi vs. 2008 issue, I was having problems setting up IET (iSCSI Enterprise Target). There is another project, a more nimble SCST - the generic (i)SCSI Target Middle level for linux. Setting up SCST is a little more complex as there is a full separation of standard SCSI emulating target from networking daemon that adds the I (as in IP based) in iSCSI. The standard SCST is a kernel module that requires full source code to compile, so if you are on CentOS, for example, the kernel-devel package is not enough to proceed. I chose to build plain vanilla 2.6.26 kernel and then build the SCST and iscsi-tgt project.

As with IET I had a same problem, system was not formatting with windows 2008. After considerable amount of time dedicated to testing, code review and communications with projects maintainers, I have figured out my issue and made it work. In retrospect I suspect that IET had the very same reason for failure as originally deployed SCST.

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More info: How I made it all work

permanent link to article http://freecash.hogger.net/windows_2008_web_edition_and_open_source_iscsi_targets

To understand, let's review my set up - I had two local gigabit full duplex cards bonded to provide both-ways simultaneous 2Gbit traffic to and from 2008 server. To further enhance the speed I had maximum jumbo packets set up on the networkcards. On linux side I had round robin bonding module set up and on windows I ran HP advanced networking with round robin full trunking set up. After numerous hours of testing it turns out that as soon as I disabled jumbo packets all started to work.

I have looked through the source code and have verified that SCST accepts jumbo packets far larger than maximum allowed by the current network card. Namely my e1000 card support 16K jumbo whereas the target software supports 256K. SCST is not to blame and most likely neither was IET. There is clearly an issue with the communications in this particular set up before it hits SCST. I will dig deeper to see if there is a problem in bonding adapter or possibly network card driver.