Disk IO for redolog buffer- isnt it a performance issue also ?

hi guys,
i am a noob but i have a curious question to ask.
hope you guys dont mind helping me out abit,
as we all know, disk io is an expensive operation, so oracle would rather keep the blocks in the db buffer cache as long as possible then to write them down everytime a commit occurs.
however
wouldnt writing and fetching from the redo log file into the redo log buffer an expensive operation as well ? especially it is a on 3 second basis ?
let say i just retrieve a empty block from my redo log file, fill in just 1 row. then it get written back to file. then again i make a update, the same block is retrieve again to fill up aganother row, then 3 second it is written back. wouldn't this be a expensive operation too ?
i know it must be done, to make sure every recorded changes make to the data blocks is written to disk as soon as possible as if we keep it long in the redo buffer, and the instance crash, we would have lost both the data and the changes recorded. so thats the only way out..
but is my theory right ?
thanks.
-noob

oraclewannabe,
redolog io is always completely sequential, and records are always appended.
datafile I/o is random or sequential.
as long as you don't locate your online redolog on i/o bound disks or raid-5 disks,
there shouldn't be a problem.
Sybrand Bakker
Senior Oracle DBA

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