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Disk Performance<br />
<br />
<br />
<br />
Rectangles in disks above represent requests queued in each individual<br />
disk of a RAID set with multiple requests outstanding (SCSI or SATA)<br />
Each disk runs the “elevator” algorithm, modified to handle rotational<br />
position, to optimize its work<br />
For skip-sequential reading, we need 20 requests outstanding for good<br />
performance, 5 in each disk<br />
This is 3-5 times faster than with 1 request outstanding<br />
But not highest MB/s: disk has to rotate between reads<br />
Note: stripe size doesn’t matter here, as long as multiple stripes of<br />
data are in play<br />
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