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Re: New Disk Utility apparently not using rdisk when saving / restoring partitions
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Re: New Disk Utility apparently not using rdisk when saving / restoring partitions

  • Subject: Re: New Disk Utility apparently not using rdisk when saving / restoring partitions
  • From: Thomas Tempelmann <email@hidden>
  • Date: Sat, 01 Apr 2017 02:02:48 +0200
Huh - I just did a test in a VM, under 10.12.3, and it was using /dev/rdisk, and was adequately fast. Yet, when I did attempt to Restore from one disk to another a few days ago, it was very slow, as if /dev/disk was used, repeatly.

That previous (slow) test was made with real Macs connected via Thunderbolt, but I don't think that should make a difference.

However, back then I ran DU from the Recovery partition. Could it be that the Recovery's DU is an older version and the new version on 10.12.3 has fixed this issue?

Has anyone else noticed bad DU performance in 10.11 or 10.12 when copying partitions, such as with using Restore or New Image from disk/partition?

Thomas



On Fri, Mar 31, 2017 at 11:51 PM, Thomas Tempelmann <email@hidden> wrote:
Not relly a file system related thing, but since I'm tired of filing bug with Apple's bugreporter and mostly just getting red tape thrown at me, I thought I bring it up here in case someone listens and wants to take reponsibility:

I found that, when using the new DU, using the Restore operation to copy a partition from one drive to another, it's unusually slow. Comparing similar operations in Terminal using the "dd" command makes me believe that DU is using /dev/diskN to read and write, whereas it should be using /dev/rdisk.

The speed difference is substantial: I had wanted to copy a 750 GB SSD from one MacBook Pro, connected via Thunderbolt Target Disk Mode to another MBP with a 1 TB SDD. With Sierra's DU (loaded from the Recovery partition) as well as with "dd" using "disk", this went along at about with less than 40 MB/s. Performing the same with "dd" and "rdisk", I got to the maximum, which was about 200 MB/s. That's more than five times slower than it should be.

I'm going to write a blog article about this over the weekend, too.

--
Thomas Tempelmann, http://www.tempel.org/
Follow me on Twitter: https://twitter.com/tempelorg
Read my programming blog: http://blog.tempel.org/



--
Thomas Tempelmann, http://www.tempel.org/
Follow me on Twitter: https://twitter.com/tempelorg
Read my programming blog: http://blog.tempel.org/
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 >New Disk Utility apparently not using rdisk when saving / restoring partitions (From: Thomas Tempelmann <email@hidden>)

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