Re: raid0 slower than devices it is assembled of?

[Andre Hedrick]

Size is MB, BlkSz is Bytes, Read, Write, and Seeks are MB/secd . -T

         File   Block  Num  Seq Read    Rand Read   Seq Write  Rand Write
  Dir    Size   Size   Thr Rate (CPU%) Rate (CPU%) Rate (CPU%) Rate (CPU%)
------- ------ ------- --- ----------- ----------- ----------- -----------
   .     2018   4096    1  244.7 53.6% 8.847 2.26% 88.04 41.7% 5.594 7.16%
   .     2018   4096    2  281.6 65.6% 11.04 3.53% 89.86 69.5% 6.645 9.78%
   .     2018   4096    4  235.6 64.3% 13.91 4.45% 88.26 96.2% 7.647 12.7%
   .     2018   4096    8  231.2 68.0% 15.91 5.34% 85.59 105.% 7.557 10.3%

Two channel, Six drives, three per channel.

U320 with 15K U160 drives in a soft Raid 0.

Andre Hedrick
LAD Storage Consulting Group

On Tue, 16 Dec 2003, Andre Hedrick wrote:

> 
> Helge,
> 
> Reads you may gain on writes only if all devices are on single ended mode.
> Both pATA and pSCSI suck wind in writes, pSCSI should smoke pATA on reads.
> It is all a matter of the physical protocol on the wire.
> 
> Only in SATA/SAS will you even reach close to ideal world.
> 
> Cheers,
> 
> Andre Hedrick
> LAD Storage Consulting Group
> 
> On Tue, 16 Dec 2003, Helge Hafting wrote:
> 
> > jw schultz wrote:
> > 
> > > No Linux [R]AID improves sequential performance.  How would
> > > reading 65KB from two disks in alternation be faster than
> > > reading continuously from one disk?
> > > 
> > Raid-0 is ideally N times faster than a single disk, when
> > you have N disks.  Because you can read continuously from N
> > disks instead of from 1, thereby N-doubling the bandwith.
> > 
> > Wether the current drivers manages that is of course another story.
> > 
> > Helge Hafting
> > 
> > 
> > -
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