3 Replies Latest reply on Oct 12, 2009 1:58 PM by Jim_Simon

    scratch disk - how big?


      Hi there, I'm looking for some info and advice.


      It would SURE be nice if Adobe put out some actual "rules of thumb" for spec'ing out a system.  Like, if your HD video project has 10GB of source material, you should have X GB of scratch disk, and if you want it in real time, your drives should handle 250MB/s (or whatever).


      But since they don't, I've got some questions.


      First, here's what we've got:


        1) Premier Pro CS4  (from the CS4 Production Premium bundle)


        2) HD video from a Sony HVR-Z5U.


        3) 2009 Mac Pro, 8-core + 8GB ram.


      The main thing I think we're lacking is a good setup of drives.  I've been desperately trying to understand what I need to get the job done without wasting money.  It sounds like we should use 3 disks (or arrays), one for OS & Software, one for scratch, one for data.   But which ones really need to be fast, which ones need to be big, etc... thats what I'm trying to plan so I can order it once and be done.  I found the following in Adobe's Premiere Pro product info:


      21. Optimize scratch disks.

      Premier Pro CS4 uses a scratch disk file (that is, temporary disk space for storing data and performing computations) when insufficient RAM is available for image editing. The hard drive partition you specify as the primary scratch disk should have free space equal to three to five times the size of the average image file; specify a secondary scratch disk if you have an additional hard drive partition. If disk space is insufficient, remove unnecessary files from your hard disk(s)


      This seems crazy small...  5 times the average image size?   lets say an uncompressed image is 20MB, times 5, just a mere 100MB.   I need a dedicated scratch disk for that?   If thats all a scratch disk is used for, it would open that in RAM, not on disk, especially with 8gb ram and 8 cores...  It almost sounds as if that was written for Photoshop, not Premiere Pro...  So I'm assuming adobe's info is bad (or I'm misinterpreting it) and we should have much more scratch than that??


      So assuming I need a lot more than that for hd video, how big does a scratch disk need to be?   My understanding is its simply for temporary files used during the edit process.   We're shooting news pieces, small feature pieces, etc..  Probably 30 minutes maximum, most of the time 3 minutes or less.  How much scratch disk space is even needed?  A couple GB?  I just don't want to buy 300GB Velociraptors or worse yet, 15K scsi, if we only need 50 GB of space for scratch.  I guess I just don't understand how much data is put onto scratch in Premiere Pro, and if its a large number, how much throughput does it need, 100MB/s ?  300MB/s ??  I need to know if the scratch should be a single 7200rpm drive, a 10K drive, a raid 0 pair, etc....?


      Oh, and how is scratch data stored?  Is it deleted whenever you close a project?  Do you manually delete the scratch data?  I just want to know that when we archive a project to storage disks that we're not storing data we don't need.   And I suppose this whole process of using different disks for project files, scratch disk, source files, etc.. that it really makes archival a little messy...


      Thanks for any input and advice!