Re: SATA RAID5 speed drop of 100 MB/s

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Sun, 24 Jun 2007, Michael Tokarev wrote:

> Justin Piszcz wrote:
> > Don't forget about max_sectors_kb either (for all drives in the SW RAID5
> > array)
> >
> > max_sectors_kb = 8
> > $ dd if=/dev/zero of=file.out6 bs=1M count=10240
> > 10737418240 bytes (11 GB) copied, 55.4848 seconds, 194 MB/s
> >
> > max_sectors_kb = 128
> > 10737418240 bytes (11 GB) copied, 22.6298 seconds, 474 MB/s
>
> Well.  You're comparing something different.  Yes, this
> thread is about linux software raid5 in the first place,
> but I were commenting about [NT]CQ within a single drive.
>
> Overall, yes, the larger your reads/writes to the drive
> becomes, the faster its linear performance is.  Yet you
> have to consider real workload instead of very synthetic
> dd test.  It may be good approcsimation of a streaming
> video workload (when you feed a large video file over
> network or something like that), but even with this,
> you probably want to feed several files at once (different
> files to different clients), so single-threaded test
> here isn't very useful.  IMHO anyway, and good for a
> personal computer test.
>
> /mjt
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Concerning NCQ/no NCQ, without NCQ I get an additional 15-50MB/s in speed 
per various bonnie++ tests.

# Average of 3 runs with NCQ on for Quad Raptor 150 RAID 5 Software RAID:
p34-ncq-on,7952M,43916.3,96.6667,151943,28.6667,75794.3,18.6667,48991.3,99,181687,24,558.033,0.333333,16:100000:16/64,867.667,9,29972.7,98.3333,2801.67,16,890.667,9.33333,27743,94.3333,2115.33,15.6667
# Average of 3 runs with NCQ off for Quad Raptor 150 RAID 5 Software RAID:
p34-ncq-off,7952M,42470,97.3333,200409,36.3333,90240.3,22.6667,48656,99,198853,27,546.467,0,16:100000:16/64,972.333,10,21833,72.3333,3697,21,995,10.6667,27901.7,95.6667,2681,20.6667

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