"Ken Blake, MVP" wrote:
> Timothy Daniels wrote:
>
>> "Ken Blake, MVP" wrote:
>>> No, raid 0 requires two or more drives. It's called striping.
>>> It puts pieces of files alternately on the several drives so
>>> you don't have to wait for the first read or write to finish
>>> before starting the next. It's for increased performance,
>>> not redundancy.
>>
>>
>> More accurately, RAID 0 does I/O faster because the
>> pieces are being done at the same time to more than one
>> drive, the read or write of each piece being completed
>> on its particular drive at about the same time as all the
>> other pieces. The speed comes from parallelism, not
>> from overlapping beginnings and ends of I/O tasks.
>
>
> Well, you said it differently than I did, but I'm not sure what
> you're describing is any different . Overlapping beginnings
> and endings achieves parallelism.


If by "read" and "write" you meant the individual I/O
commands to each drive to transfer a segment of the file
to a particular drive, yes, the individual I/O operations do
overlap (100%), and any wait for the I/Os of other segments
of a group to complete (after any one of them completes)
before starting the I/Os for the following segment group is
very short or nonexistent. That is, the I/O of segment members
of a doublet (or triplet or qudruplet, etc., depending on the
number of drives RAIDed) can be done simultaneously.
But RAID striping does not implement the overlap of the OS's
high-level READ FILE or WRITE FILE instructions. I *believe*
that those must still be done synchronously, i.e. a high-level
WRITE FILE must complete before a READ FILE on the
same file can commence. Please correct me if I am wrong.

*TimDaniels*