Using an external drive as a scratch disk?

Discussion in 'iMac' started by kat.hayes, Jun 9, 2017.

  1. kat.hayes macrumors 6502a

    Joined:
    Oct 10, 2011
    #1
    Using a 2015 5K, I use Photoshop, Premiere and some After Effects. Will it help to use an externally connected drive as a scratch disk? If so, how much of a difference can this make?

    Thanks.
     
  2. satinsilverem2 macrumors 6502a

    satinsilverem2

    Joined:
    Nov 12, 2013
    Location:
    Richmond, VA
    #2
    Depends on what type of drive your boot drive is. If its a HDD then yes using an external SSD or even a pair of RAIDed HDDs are going to make for a very nice improvement. If however your boot drive is a SSD then it won't make much of a difference apart from possibly giving your apps more room to work. Another thing to consider is how the drive will be connected to the iMac. If you are using USB then make sure you get a drive that supports UASP to reduce headroom especially with an SSD. Thunderbolt is the ideal connection to be using for scratch disks in my opinion.
     
  3. kat.hayes thread starter macrumors 6502a

    Joined:
    Oct 10, 2011
    #3
    I have a 500GB SSD in my 2015 5K iMac. I have a Thunderbolt 2 enclosure that holds two drives that I was thinking of setting up as either JBOD or RAID 0; I figured one of the drives could be a scratch disk? I could also put in two SSD in the enclosure instead of my 7200 RPM 4TB drives.
     
  4. satinsilverem2 macrumors 6502a

    satinsilverem2

    Joined:
    Nov 12, 2013
    Location:
    Richmond, VA
    #4
    Absolutely you could use SSDs in the enclosure. just remember that with RAID 0 there is no data protection so if one drive fails the whole array goes with it so make sure you have a good backup plan even though it's only being used as a scratch drive.
     
  5. campyguy macrumors 68040

    Joined:
    Mar 21, 2014
    Location:
    Portland / Seattle
    #5
    Yes. A lot, regardless of whether the boot drive is an HHD or SSD for PS and Premier, not so much for AE.

    AE will take pretty much all of the RAM you have available - in my offices, when using AE or other apps like it, it's the only app that is used in a user profile pretty much dedicated to that app and no other applications are running (especially apps that create cache files - like web browsers/email/sync services like iCloud.

    Specify scratch disks to improve system performance (Premier)
    Optimize Photoshop CC performance (specifically "Manage scratch disks")

    Read Adobe's White Paper for optimizing for the CC apps, earlier versions of your apps should be optimized in a similar vein:
    https://helpx.adobe.com/content/dam/help/attachments/Adobe_Hardware_Performance_White_Paper.pdf

    Keep your scratch disk(s) optimized/defragmented. I suggest not using the same project disk being used for AE (and similar apps) for apps like PS/Premier - the info at those links will explain why once you see the structure of how each app uses scratch disks.
     
  6. hurtmemore, Jun 10, 2017
    Last edited: Jun 10, 2017

    hurtmemore macrumors member

    Joined:
    Jan 9, 2017
    #6
    I don't have the answer but something to keep in mind, these iMacs use PCIe SSD's, which are incredibly fast, somewhere around 3x faster read/write than a regular external SSD via USB. Thunderbolt is technically faster than PCIe, but you're limited by what the external SSD can do, so in reality it is gonna be a slower drive no matter what.

    I would use Black Magic's disk speed test to find the actual read/write speeds on your internal SSD, and look up what you can get with the external on thunderbolt. In general it's always been recommended to use a separate drive for scratch - especially for mechanical drives - though I would think at this point with PCIe, you might not actually see any real benefits with a scratch disk, might actually offer less performance. As with all this stuff there's usually no one good answer for everyone, partly depends on the type of content you're creating and how much is being written to scratch.
     
  7. cityboy-100, Jun 18, 2017
    Last edited: Jun 18, 2017

    cityboy-100 macrumors member

    Joined:
    Jun 5, 2016
    #7
    I'm considering the iMac and I have a question regarding random reads.

    When compiling modern web-app front-end javascript (webpack) the system requires thousands of tiny text files. Platter drives are terrible at this and as a result even a 13" macbook pro bests a top-end iMac in compile time.

    Is the connection or SSD used in the iMac inferior to the ones in MacBook Pro? Is it NVM-express?
     

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