RAID-3? (was: cvs commit: src MAINTAINERS)

[Pawel Jakub Dawidek]

On Fri, Aug 20, 2004 at 04:34:47PM -0600, Kenneth D. Merry wrote:
+> > PS. I wonder about read optimization, so parity component can be also
+> >     used for reading in round-robin fashion...
+> 
+> That likely wouldn't speed things up too much.  The hard drives are doing
+> read ahead anyway, so they'll usually have the data ready when you go down
+> to read the next block if you're doing sequential reads.
+> 
+> You would also spend more CPU power to reconstruct the piece of data you
+> didn't read from the disk.  That'll probably increase your latency
+> somewhat, and you would also be touching all of the data with the CPU.
+> 
+> As PHK said, it might be more interesting to do data integrity checking on
+> reads.  The problem, of course, is that you wouldn't be able to correct
+> problems, you would only be able to detect them.

Those are results from RAID3 test without one data component, so parity
has to be calculated.

RAID3 in degraded mode:
		Number of	Bytes per	Requests per
Operations	processes	second		second
----------------------------------------------------------------------
READ		3		6329500		95
READ		15		9104075		136
READ		100		10895041	163
WRITE		3		5112288		76
WRITE		15		7911875		119
WRITE		100		9104075		136
READ/WRITE	3		6097224		91
READ/WRITE	15		8307468		125
READ/WRITE	100		9773492		147

Here are already presented results of full RAID3:

RAID3:
		Number of	Bytes per	Requests per
Operations	processes	second		second
----------------------------------------------------------------------
READ		3		6329500		95
READ		15		8981047		135
READ		100		10719314	161
WRITE		3		5073263		76
WRITE		15		7467387		112
WRITE		100		8631136		129
READ/WRITE	3		6041795		90
READ/WRITE	15		8104847		121
READ/WRITE	100		9494250		142

So as you can see there are no difference in reading (actually reading
in degraded mode is even a bit faster, hard to say why).
Thread, which was responsible for XOR calculations was consuming 6-7%
of CPU on 534MHz Celeron.

PS. I removed cvs-*@ from CC. Let's continue on performance at .

-- 
Pawel Jakub Dawidek                       http://www.FreeBSD.org
pjd at FreeBSD.org                           http://garage.freebsd.pl
FreeBSD committer                         Am I Evil? Yes, I Am!
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