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disk vs rdisk, was: How to obtain the FAT serial number form a volume
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disk vs rdisk, was: How to obtain the FAT serial number form a volume


  • Subject: disk vs rdisk, was: How to obtain the FAT serial number form a volume
  • From: Chris Murphy <email@hidden>
  • Date: Wed, 29 Feb 2012 13:00:52 -0700

On Feb 29, 2012, at 10:58 AM, Mark Day wrote:
>
> If you *really* need to get it for a mounted volume, and you're willing to put up with the various limitations, and you're willing to use an unsupported technique, you can read from the "raw" device (use "/dev/rdisk" instead of "/dev/disk"; so "/dev/rdisk4s1" in your example).

I've been curious about the difference between disk and rdisk for some time, when it comes to performance. While dd is not my metric for overall performance, I notice that when using dd to create and image from a disk or volume, or write an image onto a disk or volume, there is a massive difference in performance. Maybe twice the data rate using rdisk compared to disk, across all forms of media, SSD, HDD, and even USB sticks.

However, df reports mounted volumes using disk, not rdisk, yet they don't seem to exhibit the same performance "penalty" when using Finder, or some other application, to read/write files.

I do not require an exhaustive explanation, it's more a curiosity than needing to apply something in practice.

Chris Murphy
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  • Follow-Ups:
    • Re: disk vs rdisk, was: How to obtain the FAT serial number form a volume
      • From: Mark Day <email@hidden>
    • Re: disk vs rdisk, was: How to obtain the FAT serial number form a volume
      • From: Chris Suter <email@hidden>
References: 
 >How to obtain the FAT serial number form a volume (From: Chris Driggett <email@hidden>)
 >Re: How to obtain the FAT serial number form a volume (From: Mark Day <email@hidden>)

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