In order to test the pure iSCSI processing overhead, I tried to export a 5GB iSCSI target and login to it from the same machine, so that I can compare the performance of this locally connected iSCSI virtual device with that of the physical device.
I formatted the virtual device with the ext3 file system, mounted it to a directory, and ran bonnie++ under that directory to test its performance. I used file sizes of 1GB, 2GB, and 4GB (1GB is twice as large as the memory, which is the minimum required by bonnie++), and came across various errors during the test, some are the write(2) system call errors and some even reported the file system became "read only" after writing some files. The kernel also reported a journal commit I/O error on the virtual device.
The tests can be completed when the physical device is directly mounted. So I'm guessing this is a bug of iSCSI with locally connected sessions?
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