Log file sync spike

I am trying to understand what is causing "log file sync" 5-15 minutes duration spike in my db.
What puzzles me is that I can not see spike in the other activities on my db.

It is strange that:

• "redo write time" statistics does not follow "redo synch time" at the time of the spike
• v$sysstat value of "redo write time" is half of the "redo synch time".

If "redo synch time" spike happens because of hw problems then why "redo write time" does not follow it?
If it is not hw issue then what else LGWR can be doing 50% of time(see the difference between redo write time and redo synch time) ? Or am I hitting yet another V$-bug?

Database statistics in centiseconds follows:

56,105,687 cs redo synch time from v$sysstat (1.140.674 cs redo synch time from v$sesstat)
54,796,921 cs log file sync from v$system_event

24,163,771 cs redo write time from v$sysstat

162,672 cs log file switch completion from v$system_event

Thank you in advance,
Laimis N.
Fyrirvari/Disclaimer
http://www.landsbanki.is/disclaimer

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