Sandisk Extreme 900 speed in iMac 2017 USB-C

Discussion in 'iMac' started by ASAP2019, Jul 18, 2017.

  1. ASAP2019 macrumors newbie

    Jun 29, 2017

    I just bought the Sandisk Extreme 900 1.92TB and I connect using USB-C TB3 connector. My write speed is around 430mb/sec and read is 800mb/sec. It seems I cannot get my write speed to 800 to 850mb/sec as advertised. Is it something wrong with my drive or my connection? Hope some one can share their experience. Thank you.
  2. Fishrrman macrumors P6


    Feb 20, 2009
    I went to and read user reviews on this drive.

    One said:
    "I would like to know if the cable that comes in the box (USBC) supports the 10w to give the total performance of the sdd. In the benchmark tests, using a USBC to USBA 3.0 adapter, it gives me almost 400MB / s. Using the direct connection on the USBc 3.1 to ssd with the cable it brings, on my Macbook Pro 15 "beats 2016, gives the same speed.
    EDIT: I change to ONE STAR because I buy a thunderbolt 3 (40Gbps) cable and the result is the same... See the picture..."

    "Its write speeds are sort of half but I was not getting full write speeds anyway with 900 as it was USB 3.0 to USB 3.1 instead of USB 3.1 to 3.1.
    When I use USB 3.0 to USB 3.1 connection the write speeds for both Extreme and T3 were same around 300 mb/s.
    I really wished it worked for me but the extra power requirement killed it for me as I would never feel comfortable that my drive would be read what ever I would connect it to."

    So it seems the results you're getting aren't inconsistent with the results that others get.

    In my experience, regardless of what is advertised, write speeds are always slower than read speeds. Par for the course.

    $700+ seems like too much to spend on a drive, just to "get more speed out of it" (unless one is making money from the computer and can deduct the purchase price through depreciation)...

    My opinion only.
  3. ASAP2019 thread starter macrumors newbie

    Jun 29, 2017
    Hi, thanks for the sharing. Guess nothing much I can do to boost the speed as advertised. Hope someone can achieve the speed and share here. Thanks
  4. campyguy macrumors 68040

    Mar 21, 2014
    Portland / Seattle
    OP I hate to break this to you - respectfully - you're about at the limit with that drive unless you use it for a specific workflow, and you're likely not experiencing anything out of the ordinary with your 900. I picked one up last year, specifically for use with a workstation that pretty much is dedicated to Photoshop, after reading Anandtech's short benchmarking review last year and it works very well with PS, it's being used as a scratch disk for PS and project disk for FCPX. I'm going to agree with their offering that there's something in the controller that seems to be holding back the potential.

    I bookmarked the benchmark summary page, and they offer a pretty decent but not comprehensive breakdown:
  5. btrach144 macrumors 65816


    Aug 28, 2015
    I believe I read somewhere that the RAID controller (900 is two drives in RAID 0) is very poor and only hits 800 MB/s in very certain circumstances.
  6. Hrodriguez77 macrumors member


    Feb 25, 2017
    I purchased the same ssd and iMac but haven't received the iMac yet. I also purchased this cable to go with it:

    I will test it when I'm all set up.
  7. Richard Peters macrumors regular

    Richard Peters

    Jul 18, 2010
    Surrey, UK
    Keeping an eye on this thread. I've been eyeing up one of these drives for a long time to run my Lightroom library from. Was planning on getting one when I replace my 2012 iMac.

    The Extreme 900 has been out for a long time now. Maybe it'll get an update soon like the Extreme 500's have had (great little drives btw).
  8. gekko_rumors macrumors newbie

    Jan 9, 2018
    hi, I can confirm similar results on my iMac i7 5k 2017,
    around 400 mb/sec for WRITE and double = 800 mb/sec for READ.

    what confuses me:
    when I measure with AJA under bootcamp, I get around 800 mb/sec for read AND write.
    Seems that OSX has some brakes with the extreme 900 configuration
  9. anticipate macrumors 6502


    Dec 22, 2013
    I have this drive and see the same thing. It's still plenty fast for reads though!
  10. MarckyG macrumors member


    Jan 15, 2014
    Finally I find someone else with the same problem... Something in High Sierra and APFS seems to stop the Sandisk Extreme 900 to go to it's full potential. For me it's even worse... The speedtest shows it going to 400 for a second, then dropping to 250MB/s write and staying there... really disappointing. This is on my new iMac Pro's Thunderbolt 3 port with High Sierra and APFS. On my old iMac with Sierra and HFS+ over normal USB 3.0 the write stays at around 400MB/s...

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