Fedora ARM Secondary Architecture/iSCSI

Goal

iSCSI is SCSI (Small Computer System Interface) block device support over Internet (TCP/IP). It's basically a way of doing a storage area network (SAN) using $20/port gigabit ethernet instead of $3000/port FibreChannel connections.

This may be a useful technology for providing storage to the ARM hardware devices in the build farm without attaching eSATA disks to each machine. The goal, then, was to determine if iSCSI was suitable for this application.

Kernel

To test iSCSI on the OpenRD-Client system, a new kernel was required, with iSCSI support built-in or in modular form:

• Kernel sources: the upstream kernel does not have OpenRD-Client support (though it does support the OpenRD-Base). Patched source obtained from git://repo.or.cz/linux-2.6/linux-2.6-openrd.git -- see discussion at http://groups.google.com/group/openrd/browse_thread/thread/6ec7b4b39700e114
• Cross-compiled on CDOT workstation HongKong using the AM cross-development toolchain available at http://fedora-arm.wantstofly.org/cross/
• Config file used: http://hongkong/chris/openrd-iscsi-kernel/openrd-iscsi-kernel-2.6.33-rc8.config.txt

Results:

• Kernel: http://hongkong/chris/openrd-iscsi-kernel/uImage-2.6.33-rc8
• Modules: http://hongkong/chris/openrd-iscsi-kernel/modules-2.6.33-rc8.tgz

Results

iSCSI seems to work, but only to a point:

• We can login to an initiator (netbsd-iscsi package on HongKong x86_64).
• However, under heavy load (first noticed when creating a mock buildroot cache), the target receives invalid opcodes, causing the connection to fail.
  • Experimenting with a /proc/cpu/alignment value of 3 (fixup+warn) did not clear the issue.
  • Using the exact same target with a F12 x86_64 initiator is successful.