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Why the scant treatment of Scratch Disks?

Feb 19, 2013 5:51 AM

Apologies if this has been dealt with previously (grateful for any links, if so).  I've been having a bit of a discussion over at the Elements Village on Scratch Disks.  Although when I was learing Photoshop Elements, and then later the full versions of PS 3 and then 5 Extended, none of the stuff I read seemed to stress the importance of having separate disk drives dedicated to them and not used for anything else.  I hope I'm not doing Adobe an injustice, but from memory the Classroom books didn't make it a big issue, and I don't think I even ever heard of Scratch Disks until some years ago reading Steve Caplins 'How to Cheat at Photoshop', where he does talk about how essential it is to keep the Scratch Disks separate from the main computer HD.


The Classroom in a Book, which is truly excellent and I've worked thru it religiously (so to speak) deals with Scratch Disks in a fairly short paragraph and clearly leaves the reader / student with the impression that it's fine to leave them where they are.  If I'm right (and it's a while since I completed his course) Steve also doesn't -- in his series -- pay any attention to the matter (forgive me please, Steve, if I've misrepresented you).


My question is really about the modest user like myself working on small projects.  By 'small' I mean a video lasting no more than, say, 2 or 3 minutes, tho' I know even that can generate quite huge file sizes.   But I don't start new projects with an entire video-shoot of, say, 30 minutes or so.


In other words, is it possible to make too much of a fuss about connecting external hard drives with large capacity connected permanently via USB 3.0 (at best) or 2.0 at least?  I do in fact have two ext HDs connected to my Windows 7, 64-bit, 16GB RAM i7  3.40GHz (just so you know, I'm not boasting).   I got one of these after reading Caplin's book (see above) for Photoshop scratch disk use, and the other just as a second back-up (I already had an HD as first backup)  for my photos.


But as time went on, I began to use both ext HDs for backup, and made a partition on my internal HD for Photoshop (I was advised over at the 'Village' that this wouldn't speed up the workflow).


So two questions really.  (1)  Why do the books (seem to) make no big deal out of where to locate Scratch Disks?  (Not to frighten away technophobes?!) or

(2)  Is it really so vitally important for users like myself, not working on 'blockbusters'?


Thanks in advance for enlightenment on this.  The Village helped, but I'm still in some doubt and I don't want to try their patience over there any further.  Hoping I don't try yours as well,



Milton Keynes UK

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    Feb 19, 2013 6:11 AM   in reply to gbrmk

    I've heard of people adding separate hard drive, dedicated to scratch and paging files.


    With today's modern, very fast computers, I think it's overkill. It certainly won't give you a dramatic increase in Premiere Elements performance.


    There was a time with all of these configurations mattered -- as well as overclocking processors and stripping down the operating system. And maybe it still does for hardcore gamers.


    I'm not going to fight anyone who insists on doing it. But, seriously guys, an i7 computer has thousands of times the computer power that took astronauts to the moon. Among consumer camcorder video, including AVCHD and cell phone HD video, most typical off the shelf computers can edit it without working up a sweat.


    How much firepower do you really need?

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    Feb 19, 2013 7:26 AM   in reply to gbrmk

    Glad I could help give you a bit oof peace, Brian. I really do prefer simpler solutions. Especially since, between Windows 7 and Mac OSX, multi-core processors and 64-bit operating systems, with their expanded RAM use, the world of off-the-shelf computing power is pretty impressive! No need to turn every desktop into a starship.

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    Feb 19, 2013 10:37 AM   in reply to gbrmk



    First, there are major differences between what Adobe Photoshop/PSElements refers to as "Scratch Disks," and what Adobe Premiere Pro/PrElements refers to as "Scratch Disks." The discussion below, refers to a Windows machine ONLY, as Mac's might well be very different and I do not know Mac's.


    In the Photoshop family, the Scratch Disks (often only one file, but can be multiple in some instances) are almost exactly like Windows Virtual Memory/Page File. A .TMP file, or files, is/are created in the set desitnation drive (Edit>Preferences>Scratch Disks), and it is used as an overflow for any memory, that does not fit into RAM. It is dynamic, in that it will grow, as needed, though doesn't really shrink that much, until one exits from the program, when it should be Deleted. It is a bit of a holdover from when computers had limited RAM, and especially on 32-bit OS's, where the RAM was limited to 4GB, with ~ 3.5GB used fully. Still, and even on machines with 64 - 128GB of RAM, the Scratch Disk can come into play with certain functions, like stitching very large panoramas, HDR processing, Liquify, etc.. Just like the Virtual Memory/Page File for Windows, there will be reads/writes to/from the HDD, where the Scratch Disks are located. With a mechanical HDD, this reading and writing can create a bottleneck, if the Scratch Disks are located on the same HDD, as the OS, the program, and the Windows Page File, as there can be many requests going through one controller, and the heads of the HDD can only be in one position on the platters, at one time. The read/write requests are queued up, and each in line has to wait for the previous operation to finish. SSD's are much, much more efficient at allowing multiple read/writes simultaneously, and are becoming very popular for System drives, and for Scratch Disks, especially if in a RAID configuration. When speaking strictly of HDD's, it is the bottleneck with the mechanical transfer of data, that one hopes to eliminate by spreading the I/O (Input/Output) load over multiple HDD's, through separate controllers - reads/writes to one HDD are totally unaffected by reads/writes to another HDD, so long as the CPU can process the data efficiently, and as Steve says, an i7 can do a great job of this.


    Using external HDD's for Scratch Disks can be a good plan, BUT the weak link is the connection. IMO USB 2.0 is too slow. IEEE-1394a is too slow. IEEE-1394b is getting up where the connections speeds need to be. USB 3.0 looks like a viable plan, along with eSATA, which is almost exactly like a SATA internal HDD.


    Years ago, I benchmarked an old Toshiba laptop (fast for the day) w/ single 80GB HDD and Photoshop, probably about CS. The Windows Page File was obviously on my System HDD, along with my OS (probably XP, but cannot recall now), my programs, and my Photoshop Scratch Disks. I set up an Action that made heavy use of the Scratch Disks. I plugged in a 7200RPM USB 2.0 external, and moved my Scratch Disk location to that external, then closed and relaunched PS. The processing time for that very involved Action took about 9 sec. longer with the USB 2.0 external. I repeated with an IEEE-1394a (FW-400) external, and the results came in at about 8 sec. slower. I repeated with an IEEE-1394b (FW-800), and the time to process that Action was only about 1 sec. slower. Conclusion - nothing to be gained from any of those externals, for Scratch Disk, and in the first two, there was a noticeable loss in performance. I did not have eSATA to test, and USB 3.0 had not been introduced.


    OK, now lets talk about Premiere Scratch Disks. They are actually a group of different files, and they do not provide any "virtual memory" to the program. What they do, however, is allow for the creation of various "working files," that Premiere will use, when editing. They range from the Media Cache, where one will find the Conformed Audio files (CFA's), the Waveform Display files (PEK), and MPEGIndex files. There are Captured Audio and Captured Video, along with Render Files (created to provide smoothest playback of a Timeline), etc.. Depending on what operations are being perfromed, such as an Export/Share, or authoring a DVD/BD, other files will be generated. Many of these files are write once/read many, so they are not accessed at the same level, as with PS's Scratch Disk. Again, and depending on the operation being performed, some do see a lot of read/write activity.


    Where one normally sees the biggest performance improvement is by separating their OS, programs and probably Windows Page File onto one HDD, and then the Projects and media (Assets), onto another. Note: with a 64-bit OS and 16 - 32GB+ of RAM, the Windows Page File will see less use, than with a 32-bit OS and only 4GB of RAM, so if one has a 64-bit OS, with a good allocation of RAM, the performance increase by splitting the I/O load over two HDD's, will be diminished some, but still be there. With SSD's, and especially in a RAID, the performance increase might not be noticeable, if there is any. The idea is to split the I/O processing load over multiple HDD's and controllers, so that requests for reads/writes are not queued, but are happening simultaneously, and the CPU is not waiting for them. Some users take it several steps further, by locating their output files on another HDD (often a RAID), their Audio on another, their Video on yet another (often a RAID), and the Projects and Premiere Scratch Disks on yet another. Performance will increase, the more that one splits the I/O load, BUT the increments of increase will drop down, and the impact will be much less, than just splitting the Projects and Media from the OS, programs and Page File. Users have observed (I feel mostly by general "seat-of-the-pants" observation vs real benchmarks) about a 50% increase in performance, just by splitting the Projects and Media onto another physical (do not use, or think about partitions here) HDD's. That falls, as to an observable % of performance, the more splitting one does, but true benchmarks show that there is an increase, however small it might be with multiple splitting. For this reason, I recommend at least two physical HDD's for a video-editing rig. I have not tested with large, SSD's (RAID, or not), so cannot directly address their use.


    The Assets can have an impact on performance too. Where DV and HDV (plus some other formats/CODEC's) are heavily I/O intensive. AVCHD (and any flavor of H.264) are more CPU intensive. Still, and even with the H.264 material, there are I/O intensive aspects, such as with the CFA Audio files, and then the Export/Share, or authoring operations - just less than with DV/HDV type material overall.


    Personally, I feel that Adobe should have used a different term, than "Scratch Discs" for Premiere's working files, as that term applies to something different in Photoshop, and has from day one. I might have gone with something like "Working Files," but no one asked me. Using the same term for two different sets of files is very confusing, if one has both a version of Photoshop and a version of Premiere.


    Good luck in the quest,



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    Feb 19, 2013 10:56 AM   in reply to Bill Hunt

    I THINK Bill is saying the same thing as I did.


    In the real world, when you're editing DV, HDV and AVCHD camcorder video on a home computer, all that nitromethane just isn't necessary.

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    Feb 19, 2013 11:06 AM   in reply to Steve Grisetti



    Yes, you and I are close on that. I do feel that a 2x HDD I/O setup is very useful (totally necessary? Not really, but very useful.) for ease of editing. We both agree completely (or I think we do), that with H.264 material, an i5 is about the real-world minimum for smooth editing, with an i7 being so much better, read "smoother."


    One CAN get by with a 1x HDD I/O, but will likely appreciate the performance improvement just by adding a second physical HDD, and allocating the I/O load appropriately. Lot of B-F-B (Bang for the Buck) there. With more HDD's, and more splitting of the I/O load, the B-F-B will diminish, and almost exponentially. There ARE performances increases, but whether one will notice them is debabable. Like spending really big $'s on a stereo amp/pre-amp. There will likely be an improvement in the sound, but can one actually hear it?



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    Feb 19, 2013 11:48 AM   in reply to Steve Grisetti

    I think a physical separate dedicated video drive is not overdone.

    Many people do not own a i7 (or even if they did).

    And AVCHD can be though to handle.

    Even the new very popular Gopro has proven to be a bit difficult.

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    Feb 19, 2013 12:40 PM   in reply to Ann Bens

    Before I would be forced to buy a Windows 8 computer, I bought the strongest laptop I could find.  It has an i7, 16 GB of RAM, a fast HDD, USB 3.0 ports, a graphics card and a really fast SSD. 


    I read a few articles about spreading out the assets on multiple drives and tried it.  Then I tried putting everything to do with a given project in one folder on the SSD named for that project.  My SSD is smaller than my HDD and it has most of my software on it, so I need to manage the space.


    The idea is that I can work on a project on the SSD and move the entire folder to the larger HDD or an external drive for storage.


    I'm working on family reunion video shot on AVCHD cameras that is an (unbearbly) long 70 minutes!  Outputing to an  mp4 file yesterdat was faster than watching the video.  I've got more checking to do, but it took less than an hour!


    I'll be preview for errors, editing and transcoding a few more times and trying different output settings.  Then I'll see how long it takes to made DVDs and Blu-Rays.


    The performance of the i7, lots of RAM and SSD combination appears, so far, to be better than I had hoped for.



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