I/O requests are a pain in the backside. Use perfmon to monitor the process.
If this is happening on the same database file I'd add the SQLServer:Databases:Log Growth and SQLServer:Databases:Log Shrinks counters as well. It may be its growth rate is set too low.
If the log file is large you may have to set the log type to Simple Transaction (or something like that) and manually shrink it.
Some good information here, as well. It turns into a plug for their software, but some good stuff at the top. 