Performance and Capacity
| Finally, the questions we've all been waiting for: How much storage do I need, and how fast does it need to be? There are, generally speaking, three answers to these questions: the minimalist, the realistic, and the extravagant. The minimalist answers are easy to obtain (but, as you'll see, they're only a starting point). Simply put, your storage must be capable of playing back all the real-time streams you need simultaneously, and it must be big enough to hold all the media you need for a production. For example, if you intend to capture and play back one stream of DV25 media (rendering any effects and transitions), you'll need a storage system capable of supplying at least 3.6 MB/second. If you are producing a 15-minute show rendered out as a self-contained movie and have a 3:1 shooting ratio (3 minutes captured for every minute in the finished piece), you'll need 1 hour of DV25 storage: about 13 GB. If instead you need to play back three real-time streams of DV50 material without rendering, you'll want to provide storage with 3 times DV50's data rate of 7.2 MB/second, or 21.6 MB/second. You can use the tables at the end of this lesson to deduce the requirements for many of FCP's media types; for any not listed, render a 1-minute Timeline using the appropriate codec, frame rate, and frame size to derive the necessary numbers: measure the resulting file size and multiply by 60 for the storage needed for an hour; divide by 60 to get the required data rate per second. For third-party codecs, try downloading the software codec from the vendor's Web site and running the same test. Note DV and uncompressed codecs do not vary in their bit rates or storage requirements depending on scene content, but many other codecsincluding Photo-JPEG and Motion JPEGdo. Such codecs can vary in their data rates by a factor of five based on scene complexity. To be on the safe side, render your tests using FCP's noise generator (in the pop-up menu, lower-right corner of the Viewer), or try capturing typical footage through your capture card and saving it using your test codec. The calculations get a bit more complicated with shared storage like Xsan systems, since you have to consider multiple workstations accessing the storage at the same time, perhaps using media with different bit ratesone fellow wanting six streams of DV25 while another expects two of DVCPROHD 24p. Even so, it's easy enough to calculate the answers for each workstation alone and then add them together to get the total requirement. Simple enough, isn't it? Unfortunately, the minimalist answer rarely suffices. FCP accesses data in a "bursty" manner, not a continuously smooth-flowing stream, and storage subsystems that just barely meet sustained transfer requirements can't keep up if they have to seek rapidly and frequently from one clip to another. A drive that plays back a single clip on the Timeline for hours at a time may cause dropped frames when presented with a Timeline comprised of rapid-fire cuts. By the same token, "just enough" storage is rarely enough. Even that 3:1 15-minute show will have intermediate renders, alternate versions of portions of the Timeline, and associated graphic files, sound effects, Soundtrack loops, Live Type titles, and Motion compositions, pushing its storage requirements beyond those suggested by the simplistic minimalist calculation. The realistic answer is that you need to provide a margin of performance and capacity above the minimalist requirements. How much margin is open to interpretation; it's accepted practice to set the requirement for DV25 drive performance at twice the minimalist bit rate, but it's unclear if you need a full 2x margin for uncompressed HD production. Nonetheless, the general consensus appears to be that providing twice the required sustained bandwidth gives you enough margin for safety, regardless of the media type you're using. Following this rule, calculate the minimalist answer as described earlier in this section, multiply by two, and provision bandwidth accordingly. For capacity calculations, a similar judgment can be made, although it's more subject to variation depending on your FCP workflow patterns. Some editors work very abstemiously; others produce render files, alternate versions, temporary graphics, and sound mixes with wild abandon. For the former, providing twice the minimalist capacity may be more than enough; the latter may take five or more times the calculated storage. Realistically, plan using the factor of two, and adjust as necessary based on expectations and experience. Finally, of course, there's the extravagant answer. In the words of an old MTV motto, "Too much is never enough." Practically speaking, there's more than a grain of truth in this answer; whatever storage you plan for today will come to seem too small and too limiting down the road. Parkinson's Law applies to bandwidth and storage just as to time: whatever you provide today will be filled tomorrowor if not tomorrow, the day after. Data Rates and Storage Requirements for Common Media TypesWe rendered out 1-minute tests from FCP itself using the specified settings to derive these tables. Each clip had two channels of 16-bit 48 kHz audio in addition to the video track. Captures in the corresponding formats should be very close to these numbers, but may differ slightly due to different QuickTime packaging strategies used on captures compared to renders.
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