12 Replies Latest reply on Sep 12, 2009 10:12 AM by the_wine_snob

    question about drives


      hello again

      I started editing some concert video today - lot's of motion and lighting changes. the clips are AVCHD, which as you know gets more and more difficult to decode as motion increases (or so I was told).

      I'm using a G-raid drive. the picture is stuttering - unacceptably so. just on a hunch I copied the clips over to my system drive - presto, no stuttering.

      I ran xbench on both drives - it says that the raid is faster on all counts (see results below).

      I backed up all the data on the raid, reformatted it using mac drivers, and copied just a few clips back over to it - same exact performance.

      I'm working on a macbook pro 2.4 ghz intel core duo, yeah yeah, I know it's underpowered, but it works fine for 90% of what I do.

      Just wondering if someone can tell me why the supposedly faster raid is choking....



      mac system drive test Results 120.18


      Disk Test 38.96

      Sequential 72.34

      Uncached Write 95.57 58.68 MB/sec [4K blocks]

      Uncached Write 95.78 54.19 MB/sec [256K blocks]

      Uncached Read 39.37 11.52 MB/sec [4K blocks]

      Uncached Read 111.29 55.93 MB/sec [256K blocks]

      Random 26.66

      Uncached Write 8.94 0.95 MB/sec [4K blocks]

      Uncached Write 73.45 23.51 MB/sec [256K blocks]

      Uncached Read 65.15 0.46 MB/sec [4K blocks]

      Uncached Read 108.62 20.16 MB/sec [256K blocks]


      G-raid drive test:


      Drive Type Hitachi HDP725050GLA360

      Disk Test 87.27

      Sequential 90.29

      Uncached Write 103.62 63.62 MB/sec [4K blocks]

      Uncached Write 99.73 56.43 MB/sec [256K blocks]

      Uncached Read 56.59 16.56 MB/sec [4K blocks]

      Uncached Read 143.90 72.32 MB/sec [256K blocks]

      Random 84.45

      Uncached Write 40.20 4.26 MB/sec [4K blocks]

      Uncached Write 183.00 58.59 MB/sec [256K blocks]

      Uncached Read 109.39 0.78 MB/sec [4K blocks]

      Uncached Read 126.85 23.54 MB/sec [256K blocks]

        • 1. Re: question about drives
          Jim_Simon Level 9

          Best guess is the path between the external and memory isn't fast enough, even though the drives themselves may be faster.

          • 2. Re: question about drives
            the_wine_snob Level 9

            Can you not put the media files onto one of your internal HDD?


            What is the connection of your G-RAID array?


            Good luck,



            • 3. Re: question about drives
              funkygh Level 1

              yes, hunt, I can keep the footage on my internal drive, up to a point. it's only 250gigs.

              I was more asking since the raid is supposed to be the solution for video editing and it's performing pretty poorly.

              it's connected via FW800....



              • 4. Re: question about drives
                the_wine_snob Level 9

                I use FW-800 for SD material, but would be very cautious with AVCHD, because of the processing time. Yes, it is more CPU intensive, than most other footage, that relies more heavily on I/O sub-system for playback.


                This would be a potential bottleneck that I would look into.


                How does the internal HDD material playback?


                Good luck,



                • 5. Re: question about drives
                  funkygh Level 1

                  the clips play back fine from my internal drive. I can always work that way. wish I'd known before buying the raid - could have gotten 3 times the storage for that money. but that's how it goes in video world....

                  • 6. Re: question about drives
                    Jim_Simon Level 9
                    it is more CPU intensive, than most other footage, that relies more heavily on I/O sub-system for playback.


                    How so?  The data rate is actually less than DV, so the disk system is less taxed, not more.  Once the data is fed to memory, it's all CPU dependant.

                    • 7. Re: question about drives
                      the_wine_snob Level 9



                      Not sure what you are saying here.


                      Is it that the I/O sub-system plays no role in the playback of video files, and it is only the CPU?


                      Or, are you saying that AVCHD does not tax the CPU?


                      I'm not clear on your point.





                      • 8. Re: question about drives
                        Jim_Simon Level 9

                        My point was that AVCHD is no more taxing on the disk system than DV due to it's data rate.  Much more CPU intensive, to be sure.  But not especially disk intensive.


                        Looking back over your post, it's possible that I misunderstood your original meaning.  (Your comma heavy style confused me.)

                        • 9. Re: question about drives
                          Colin Brougham Level 6

                          Disk drives and the relevant architecture that gets the data to the processing "guts" of a computer doesn't mean much of anything in relation to the decompression and playback of a video stream. The disks and I/O simply feed the data to the processor, etc., and then those components do the heavy lifting. AVCHD tops out at a datarate of 24Mbps, which is less than DV's 25Mbps, and those are both well within the capability of any modern hard drive to spool out. But since AVCHD is so much more compressed (meaning, it has to be "blown up" in order to be played back), it needs significantly more horsepower to playback and edit than DV, or even DVCPROHD at 4 times the datarate.


                          It's a reciprocal relationship: the more compressed the video, the less data transfer rate is needed, but the more processing power is required. The less compressed the video, the more data transfer rate is required, but processing requirements go down. For example, uncompressed video (SD or HD) requires massive data throughput, but is actually very easy for a computer to playback, as there is no decompression going on. The opposite is true for AVCHD and the like.

                          • 10. Re: question about drives
                            Jim_Simon Level 9

                            Well said, Colin.

                            • 11. Re: question about drives
                              the_wine_snob Level 9

                              The point was that with many formats/CODEC's, the I/O sub-system is more critical to overall playback operation. With AVCHD, the heaviest role is placed onto the CPU.


                              Sorry if I confused you,



                              • 12. Re: question about drives
                                the_wine_snob Level 9



                                I agree completely.


                                Now, so long as the I/O sub-system is not burdened with other tasks, playback should be easy. It is when one has a single HDD, and it is called upon to do much more, that issues often occur. With a properly setup and implemented I/O sub-system, playback should not be a problem - with the exception to follow.


                                AVCHD, and other heavily-compressed formats/CODEC's do tax the CPU more. If the CPU is weak, the best of Harm's I/O setup will not help.