how to determine the amount of hard drive throughput you need?

Discussion in 'Digital Video' started by videoed, Aug 25, 2010.

  1. videoed macrumors regular

    Joined:
    Mar 1, 2009
    #1
    Hi,

    just wondering how to best determine how much throughput I will be needing when I purchase new hard drive.

    is it basically the data rate of my video files multiplied by the maximum number of concurrent video streams i ever need

    plus a little more for things like static graphics and the random motion video transition etc?

    how do you do it?

    thanks
     
  2. martinX macrumors 6502a

    martinX

    Joined:
    Aug 11, 2009
    Location:
    Australia
    #2
    It depends if your OS is on the same hard drive as well.

    If you are talking about ProRes high def files, don't expect to get too many concurrent streams over a standard bus.

    On my iMac's internal HDD, I can get 4 AIC 1920 x 1080 streams at once.

    In the white paper on Pro Res, Apple get 3 concurrent ProRes streams on a Macbook Pro 7200 RPM drive (which also has the OS on it).

    You can increase the number of streams by reducing the playback quality. Apple states that "medium quality" is essentially a half-size rendering.
    "Optional half-resolution playback for even better real-time performance. When real-time playback in Final Cut Pro is set to medium quality, ProRes 422 is decoded to half of the horizontal resolution and half of the vertical resolution. This produces more real-time performance for e∂ects, transitions, and multistream playback."

    You will always want more :)

    How do you plan on connecting the HDD to your system?
     
  3. videoed thread starter macrumors regular

    Joined:
    Mar 1, 2009
    #3
    i'm looking at a RAID 5 to be connected through esata that claims to be able to deliver roughly 240MB/sec and would be using this only as a media drive- to include still graphics, motion graphics and video.

    i've been told the codec we will be moving to would be roughly 25MB/sec and we rarely have more than 2 streams of video playing at a time and a vast majority of the time, only 1 stream.

    still graphics are frequent and motion graphics are short and don't appear too terribly often.
     
  4. martinX macrumors 6502a

    martinX

    Joined:
    Aug 11, 2009
    Location:
    Australia
    #4
    Sounds like you'll have plenty of wiggle room then.

    Don't forget, RAID5 isn't built for speed. While this may not be a problem, a quote from Barefeats (in 2005) is worth remembering:

    So is RAID 5 fast enough? At first glance at the Blackmagic and DiskTester results, I was impressed. Though slower than RAID 0, I expected lower sustained transfer rates than those observed. According to the AJA Kona System Test, you should be able to playback 3 streams of 1280x720 10bit video with our five drive RAID 5 setup. HOWEVER.... those estimates are based on an AVERAGE read rate of 225MB/s. If you examine the raw data for individual video frames, the transfer rate fluctuates wildly, dropping as low as 62MB/s. Can you say, "dropped frames" boys and girls?

    When we configured the same drives as RAID 0 and reran the Kona test, the average READ rate was 278MB/s (or 4 streams). And looking at the raw data, the rate for individual frames never dropped below 216MB/s (or 3 streams).

    RAID 5 isn't ideal for a Photoshop Scratch Volume either, based on our test which forces Photoshop CS to rotate a 500MB file with only 250MB of memory cache. I know for a fact that Photoshop writes to the Scratch Volume using tiny transfer blocks. That means the RAID 5 set is going crazy writing parity data as well as making a copy of your rotated image.

    IMHO, RAID 0 is still the preferred mode both HD Video and Photoshop Scratch. If you don't want to be bothered with backup and don't want to give up any speed, you can always double the number of drives and use RAID 0+1.
     

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