Multiple log groups per thread to improve performance with high redo writes

I am reading Pro Oracle 10g RAC on Linux (good book). On p.35 the authors state that they recommend 3-5 redo log groups per thread if there is a "large" amount of redo.
Who does having more redo log groups improve performance? Does oracle paralelize the writes?

redo logs are configured per instance, from experience you need atleast 3 redo log groups per thread to help switch over and sufficient time for archives to complete before reuse of the first redo log group. When you have a large redo log activity there is a potential that redo log groups will switch more often and it is important that archive has completed before an exisiting redo log group can be reused, else the database /instance may hang.
I think that is what the author is referencing here, have sufficient redo log groups (based on the acitivty of your environment) to allow switching and allowing sufficient time for archives to complete.

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>
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Multiple log groups per thread to improve performance with high redo writes

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