How fast can the computer grab the data ? (related to storage)

Discussion in 'Mac Pro' started by rueyloon, Sep 2, 2014.

  1. rueyloon macrumors regular

    Sep 24, 2013
    Split from another thread.


    About the speed of storage, how fast can the computer grab the data anyway ? If you factor in processing time, is storage still the bottle neck ?

    Assuming a READ, PROCESS, WRITE cycle like for photoshop batch processing, which takes 0.5 seconds, 3 seconds, 0.5 seconds. If storage is twice the speed, it would only shave 0.5 seconds off the overall time taken, that's assuming the computer can even grab the data at twice the speed.

    Where is the current practical limit where you won't see any real life difference ?
  2. jdiamond macrumors 6502

    Dec 17, 2008
    Try tests with a RAM disk...

    I usually answer this information by grabbing a free utility and creating a temporary RAM disk on my computer. Of course, you can't do full scale tests, because what you're doing must fit in your ram disk and in the remaining RAM of your computer. But it reveals a lot. It acts as a "limit case" - how fast would your workflow go if you had a fast hard drive.

    The thing about hard drives is they don't matter all the time, but when they do, it's typically an "all stop" while waiting for them.
  3. jdiamond macrumors 6502

    Dec 17, 2008
    I just ran Black Magic Design's Disk Speed Test on a 6GB RAM Disk

    For perspective, I just created a 6 GB RAM Drive using RamDiskCreator, then ran Black Magic Design's iconic Disk Speed Test on it. Both read and write sustained rates above 1.2 GB/second. (The DRAM is of course much faster than that, but I guess emulating a mounted hard drive adds a lot of overhead.)

    The RAM disk results are as fast as any SSD RAID result I've ever seen, so it's a pretty good way to say, "what if I had an awesome hard drive?"
  4. h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    For info, you can achieve a much faster speed with RAM driver.

    DiskSpeedTest RAM driver.png
  5. goMac macrumors 603

    Apr 15, 2004
    Drive speeds are nowhere near data processing limits for a computer. The current Mac Pro SSD, which is near the top end of SSD speeds, uses two PCIe lanes and I don't think quite maxes them out.

    A graphics card on the other hand uses 16 PCIe lanes. If you ever had a situation in which you were loading a serious amount of data from a drive onto a GPU, it just wouldn't be close, the GPU would be way faster.

    So no, drives aren't anywhere close to the processing limits of a computer, and yes, there are lots of situations in which a drive can make a huge difference. Some posters in this thread were talking about RAM speeds, which has even more throughput than a GPU, and is even faster than an SSD.

    When will we hit a limit when data transfer speed doesn't matter anymore? When files stop growing in size, and everyone's drives are fast enough. So far that hasn't happened yet. A lot of disks still have trouble working on uncompressed high resolution video.
  6. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC

    Storage is still a bottleneck as the RAM disk guys have pointed out. So the first thing you need do if optimizing I/O performance is make sure you have more than enough RAM because OS X wisely uses untapped RAM for a disk cache.

    And as you already mentioned, storage is only a bottleneck when stuff is being read/written, but when this is happening, the difference can be dramatic. Storage performance can be be a huge factor in overall system performance. Stated another way, upgrading your storage can be one of the biggest improvements you can make to your overall system performance.

    So, get an SSD.

    Now, what makes the most difference when optimizing storage systems?

    1. RAM (as I mentioned above)
    2. Medium (SSD is much better than HD)
    3. Storage interface (SATA, PCIe, etc.)

    Will you notice the difference between an SSD and an HD?
    - Absolutely... SSDs are orders of magnitude faster than HDs at random I/O which represents the bulk of single-user workloads.
    Will you notice the difference between the latest SSD and last years model?
    - Not likely.
    Will you notice the difference between brand X and brand Y SSD?
    - Not likely.
    Will you notice the difference between a pair of SSDs in RAID0 and a single SSD?
    - Not likely.
    Will you notice the difference between a SATA2, SATA3, or PCIe SSD?
    - Not likely.

    Why? Because in all of these last 4 cases, the small block random I/O performance is very similar.

    Don't pay attention to sustained transfer rates of 500GB/s or 1000GB/s... as you point out, the opportunity to use those data transfer rates are far and few between and generally either don't last long enough to be a burden (copying a photo or video) or are so long (backup 1TB disk) that the they call for a coffee break regardless of the storage.

    The real story lies in small block (e.g. 4k) random I/O where all SSDs are pretty similar. This is where booting, loading apps, loading projects, saving projects, and scratch really benefit.

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