Optimizing Linux with cheap flash drives

Posted Feb 18, 2011 22:49 UTC (Fri) by jengelh (guest, #33263)
In reply to: Optimizing Linux with cheap flash drives by ewen
Parent article: Optimizing Linux with cheap flash drives

>and modern drives are used with constant linear velocity.)

I beg to differ. CAV (with zoned recording), please. You know the horrid seek times of CLV as used with CD-ROM.

Optimizing Linux with cheap flash drives

Posted Feb 18, 2011 23:44 UTC (Fri) by ewen (subscriber, #4772) [Link] (1 responses)

Yes, "zoned CAV" was what I had in mind when I wrote "constant linear velocity" for modern hard drives: the idea being that in the areas where there's more media passing under the head, you can have higher bit density than in the areas where there's less media passing under the head. But as you point out trying to optimise this on a per-track basis is horribly counter productive.

I probably should have said "semi-constant" linear velocity (the "zoned CAV" term didn't even come to mind until you pointed it out).

Ewen

Optimizing Linux with cheap flash drives

Posted Feb 2, 2014 3:20 UTC (Sun) by jzbiciak (guest, #5246) [Link]

It's not really constant linear velocity, as you can't speed up and slow down the rotation of the disk platter nearly fast enough. That's what the early CD-ROMs used to do, and seeking sucked because not only did you have to move the head, you also had to accelerate the media. Hard drives don't do that. The only time I hear my hard drives change rotational velocity is when I power up or power down my machine.

Rather, the bit-rates speed up at the outer edge of the disk and slow down as you move in, giving you a relatively constant areal bit density. The platter moves with constant angular velocity (ie. 5400 RPM, 7200 RPM, what-have-you), and the bit-rate varies by zone.