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Photoshop Scratch Disks - Cutting through the crap...

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February 17, 2007 7:47:30 PM

I am looking for the opinion of a knowledgeable Photoshop user who really knows their scratch disks. I've looked high and low for an answer to this question, and I cannot find a definitive answer anywhere... not on Adobe's website or after a thousand Google searches.

NOTE: If you've *heard* something about scratch disks or remember some benchmark from somewhere, it would be more helpful if you just don't reply. Even if you've built your own PS rig and used a 74GB Raptor... this does not make you knowledgeable in the matter just because you've noticed that Photoshop runs faster than the 3-year-old computer you just upgraded from.

What I'm wondering is how much scratch disk space does PS actually *use*? I have read a vast range of opinions that span every possible scenario... so it seems like no one knows what they are talking about. Here are some of the recommendations I've come across:

- Photoshop only uses 1.5x the amount of RAM you have for the scratch disk. If you have 2GB RAM, you only need a 3GB scratch disk.
- All you need is an 8GB partition on your data drive that's separate from the OS page file.
- A separate 20GB hard drive is all you need... speed is not an issue.
- A separate 37GB Raptor is just the ticket
- Two cheap 40GB drives in RAID 0 gives you better speed than an expensive Raptor
- The fastest 74GB Drives you can find. The more the better. PS scratch disks are a hog

Can someone help me cut through the crap and provide a knowledgeable answer about scratch disks?

- How much space do you need?
- Do you see big performance gains in *Photoshop* when you run the disks in RAID 0? Is that even necessary?
- In what scenario would you see the highest possible SD usage you can think of?

Please provide references, if possible. Thank you!
February 18, 2007 3:44:51 AM

I would imagine you are stressed, because I was in your shoes a while ago, but you need to ask for help a little more nicely.

As far as Photoshop goes, I think you are going about this the wrong way. Scratch disks are not the way to go to improve Photoshop performance. You should look into a 4GB system with 64bit OS. Photoshop can take up to 3GB max of your memory, and there have been benchmarks done on a Mac that show that there are noticeable speed boost when jumping from 2GB to 4GB when dealing with heavy files. However, after 4GBs, there is no boost. Again, this has to do with the limit photoshop has.

Photoshop will only use a scratch disk when it runs out of memory. When you create virtual RAM on your HD, it doesnt matter if you have 5 Raptors or Atlas in RAID 0, RAM is always going to be faster, hence my recommendation.

Now that CS3 is on its way, the whole thing changes. You get a full 64bit application that should take full advantage of the 64bits, much higher limit for RAM, and a Core 2 Quadro. That means you can go crazy and get an 8GB system along with a Kentsfield to maximise Photoshop.

Hell, I currently have 1.5GBs RAM and a Raptor 150 as my scratch disk cause im too lazy to format and instal XP on it, and trust me, using the scratch disk is no fun at all, Id rather have the 4GB. I opened a JPEG thats 24000 x 26700 yesterday and my system just could not handle it, even with probably one of the best scratch disks you can have. So I reiterate, get RAM first, processor second, and you wont even need to deal with scratch disks and their slowness.

However, if you deem HDs are the cheeper way to go, then you should not use 2 Satas in Raid 0, because as benchmarks have shown, they are not faster than a single Raptor 150. I dont know where you got that information. Maybe price/performance, it would be better, but not in sheer performance. And I seriously doubt that they will increase performance by any large amount since like I stated as you can see by the example I used above. RAM is always faster. Also, scratch disk should never be on the same HD as your OS, not even if its a seperate partition.
February 18, 2007 4:27:00 AM

gentrinity, thanks for the reply.

I have already decided on the E6600 and 4GB of PC6400 DDR2 800 (for overclocking). So no problems there... Also, I'm sticking with 32bit XP for now, so I can't use more RAM even if I wanted to.

I understand that writing to a Scratch Disk is no substitute for high performance RAM, but this is exactly why I need to setup the fastest possible scratch disks for photoshop. I regularly work with PS files of 100MB to 600MB. Many of these files can be opened at once with many active filters and long history states for each. I'm positive that photoshop will need to use a scratch disk. But my big question is just how much data will photoshop write to the scratch disk?

Is it possible for Photosop to use upwards of 80GB of data for a scratch disk? I have a hard time believing that photshop could use even 20GB. I've tried so hard to find an answer to this... no one has been able to offer a reliable answer about how much data photoshop will write to the scratch disk. Not even the Adobe FAQ.

This is important for me to figure out because there are so many ways to setup a scratch disk. If it's actually possible for photoshop to use 20GB of scratch space frequently or at least on average then I will happily purchase a low capacity Raptor or maybe even SCSI drive.

If scratch disks can grow as big as 80GB then there are a number of other options. I could get a single 74GB Raptor, or two 37GB Raptors setup in RAID 0, or two 37GB Raptors assigned as separate Scratch Disks in Photoshop, or I could save money and get two high performance 7200 80GB drives and set those up in RAID 0.

You can see how this becomes a big headache. Until I can find out definitive answers about scratch disk usage, scratch disk performance, benchmarks etc... I can't commit to any kind of purchase.
Related resources
February 18, 2007 1:26:56 PM

http://forumz.tomshardware.com/hardware/modules.php?nam...

Thats a topic I started a while ago. I quote the Adobe site.

It recommends RAID 0, but to be honest, its not the RAID, its the transfer speeds, thats the most important part. Two cheap 7200RPM drives cannot beat a single Raptor

http://www.tomshardware.com/2006/02/06/wd1500ad_raptor_...

You can see that there.

Getting a Raptor for a scratch disk is probably your best bet for some faster Photoshop experience, and definately putting it in a RAID would be even better. But I will tell you again, my Raptor 150 scratch disk is still very noticeably slower than when I am using my RAM. Hell, maybe having a E6600 would change all that, but still.

Also, even though I do not have the hard data, I assure you, there is no way in hell Photoshop will take 80GBs of HD space. Thats just impossible. I think the most it can take are 2-4GBs.

Also, I ask you something, are you getting 2x2GB or 1x4GB?

Your decision to stick with 32bit is also going to hinder your performance. I would suggest you set up a dual boot in your system so you can have both, the 64bit just for Photoshop, and then have your 32bit if you have peripherals and stuff that do not run on 64bit. Even though Photoshop CS2 isnt 64bit, the better memory management of the 64bit system is still good enough to give PSD a nice little performance boost. CS3 is going to be a monster under a 64bit system.

Also, remember that having 4GBs does not allow you to give PSD the full 3GBs it can take.

Sorry man, but I just cannot recommend HDs over a 64bit system with more RAM. I just cant.
February 18, 2007 5:21:09 PM

gentrinity, thanks again for your reply.

That would be great know if photoshop is guaranteed to use less than 10GB of scratch disk.

Since the scratch disk uses so little space, what else are you putting on your 150 Raptor? I thought a scratch disk had to be totally empty from anything else to work best. What kind of data do you save to all that extra space? Certainly not the OS... but perhaps the applications? Or do you just store as many PSD files on there as you can?

Also... maybe I will look into 64bit XP. But I am worried that I will not find all the drivers that I need. Perhaps the dual boot solution will work. I will look into it.

As far as RAM is concerned, I think I might actually be getting 4x1GB... but I am open to other suggestions if it makes sense to do something else. As far as I understand, 2GB sticks do not perform as high as 1GB sticks.

Also... you say that having 4GBs does not allow me to give PS the full 3GBs it can take... how much do you need then?

Thanks so much.
February 18, 2007 6:47:49 PM

Yeah, the Gigabyte solid state drive.

You know what, that is your best bet for a great HD. You are 100% correct on that.

http://www.newegg.com/Product/Product.asp?Item=N82E1681...

Keep looking for it. Its a lot faster than any raptor and I have seen benchmarks on Windows Boot, blows all other HDs out of the water.

However, it can only go up to 4GB, which is not great for OS and Apps, but perfect for a scratch disk.
February 18, 2007 7:00:52 PM

Quote:
Since the scratch disk uses so little space, what else are you putting on your 150 Raptor? I thought a scratch disk had to be totally empty from anything else to work best. What kind of data do you save to all that extra space? Certainly not the OS... but perhaps the applications? Or do you just store as many PSD files on there as you can?


I just have a bunch of files and I was using it to boot Vista RC2, but I didnt like it so I stopped using it and just used it as a scratch disk. The drive does not have to be empty, but it should, as it increases the performace of the HD. The idea is to keep the virtual page seperate from the scratch disk.

Quote:
Also... maybe I will look into 64bit XP. But I am worried that I will not find all the drivers that I need. Perhaps the dual boot solution will work. I will look into it.


That is exactly what my friend is doing. He set up 32bit and 64bit, and normally uses 64bit until he needs to use a printer or something. So please consider that above everything else.

Quote:
As far as RAM is concerned, I think I might actually be getting 4x1GB... but I am open to other suggestions if it makes sense to do something else. As far as I understand, 2GB sticks do not perform as high as 1GB sticks.

Also... you say that having 4GBs does not allow me to give PS the full 3GBs it can take... how much do you need then?


I do have a suggestion;

http://www.newegg.com/Product/Product.asp?Item=N82E1682...
or
http://www.newegg.com/Product/Product.asp?Item=N82E1682...

This will allow you to overclock. I have heard from numerous people on these forums that OCing with 4 sticks is not conductive to good results. Having 4GBs on 2 sticks will help, especially since they are DDR2 800. Also, this will allow you to get 8GBs in the future if you start doing heavy multitasking while still being able to allow maximum RAM usage for all apps, then you will have to trade some CPU power for more RAM.

Also, I never said you couldnt get the full 3GBs on PSD with 4GB, I said you cannot get the full 3GBs on PSD with 4GBs on a 32bit system. 32bit system will not recognize more than 3GBs, the other 1GB is used for the system virtual whatever. Point is, get 64bit, cause then you can definately use all of the 3GB limit. Also, remember CS3 is coming around, that app is going to kick so much ass.
February 18, 2007 8:06:04 PM

gentrinity

Thanks so much, you've been very helpful. I will take everything you've said into consideration.

After my last post I was still wondering about scratch disks, so I thought I would email my question to Bert Monroy. He is the creator of the massive Photoshop project called Damen, and he also hosts a podcast on Revision3.com.

To my surprise, he replied within 20 minutes of my email. Although he did not provide me with exact recommnedations about scratch disk sizes, he did mention that he personally uses 250GB spread out over several disks just for scratch space! This is what he said:

Quote:
How much scratch disk is used depends on many factors. The most
important is the amount of History states you have set. The more
states, the more space you need. Remember, an entire version of the
image is stored in memory to be accessed once you hit the Undo botton.
If you have multiple files opened it will make it worse.

I have 250 gigabytes assigned as scratch disk space, spread out over
several disks. My files tend to be quite large.


Crazy, eh? I might just get that 74GB Raptor after all. But the i-RAM is also looking very tempting!
February 18, 2007 8:36:20 PM

I don't know anything about photoshop, but I am a computer engineering student, and I know for a fact that more than 2GB or about 2.5GB of ram on a rig with a 32bit winXP will be wasted. The reason for this is because there are approximately 4billion places that the operating system can potentially address in memory, and so windows must set aside or sacrifice some of these potential addresses in RAM for I/O devices, and windows puts aside a pretty huge chunk of those 4billion places for devices. If you are having trouble understanding why these addresses must be set aside, look up "Memory-mapped I/O" on wikipedia and it will explain it all. The moral of the story is that if you NEED 3GB just for photoshop stuff, you aren't going to be able to pull that off on 32bit winXP because it will not use/recognize all 4GB. You will need to get the 64bit version of windows if you want to take advantage of all that ram.

Bearing that in mind, kudos to gentrinity for suggesting the 64bit windows. That was the smart thing to do.

-Zorak
February 18, 2007 9:50:49 PM

Thanks Zorak, I tried explaining what you just said, but obviously, not anywhere close to the technical grace you exhibited.

@dawgma

The i-Ram is a smart choice, however, it is the more expensive one. Cause itll cost you about $400 to set up a 4GB HD. For that amount of money, Id rather get another 4GB kit, which only costs about 40 more dollars and you know very well you will get more speed with the extra RAM. The 74GB Raptor is also a nice choice, however, and the guy you emailed has a point in that you can distribute to various scratch disks. So lets look at the options assuming you are already getting 4GBs;

Under $440

a.) 2x2GB DDR2 800 = $420
b.) 4x1GB DDR 400 + Gigabyte i-Ram = $420
c.) Raptor 74GB HD x 3 = $440

They are in order of the best performance.

We have never even discussed your price range. Do you have one?
February 20, 2007 5:16:03 PM

My budget is pretty loose actually...

I have already decided that my data drive will be 4 7200RPM drives in RAID 5. This array will cost about $550. The RAM that I'm looking at (4GB) will put me back another $600. So I would say I have between $800-$1000 CDN (~$650-$800 USD) to to figure out what I want to do with the OS drive and scratch disks.

My main goals are to have reliable and fast read data drives, as well as a super-fast OS performance.

With regards to using the iRam as a scratch disk, I've done a little more research on it. Apparently the guys over at AnandTech didn't think it helped too much:

http://www.anandtech.com/storage/showdoc.aspx?i=2480&p=...
Quote:
Adobe Photoshop is a slightly different creature as it keeps a scratch disk that is separate from the Windows pagefile. We tested Photoshop and used the i-RAM as our scratch disk, but in all cases it always made more sense to just throw more memory at Photoshop to improve performance where we ran out of memory.


I also found this quote on the Adobe site about how Photoshop uses RAM:

http://www.adobe.com/cfusion/knowledgebase/index.cfm?id...
Quote:
When you run Photoshop CS2 on a computer with a 64-bit processor (such as a G5, Intel Xeon processor with EM64T, AMD Athlon 64, or Opteron processor), and running a 64-bit version of the operating system (Mac OS v10.3 or higher, Windows XP Professional x64 Edition), that has 4 GB or more of RAM, Photoshop will use 3 GB for it's image data. You can see the actual amount of RAM Photoshop can use in the Maximum Used By Photoshop number when you set the Maximum Used by Photoshop slider in the Memory & Image Cache preference to 100%. The RAM above the 100% used by Photoshop, which is from approximately 3 GB to 3.7 GB, can be used directly by Photoshop plug-ins (some plug-ins need large chunks of contiguous RAM), filters, actions, etc. If you have more than 4 GB (to 6 GB (Windows) or 8 GB (Mac OS)), the RAM above 4 GB is used by the operating system as a cache for the Photoshop scratch disk data. Data that previously was written directly to the hard disk by Photoshop, is now cached in this high RAM before being written to the hard disk by the operating system. If you are working with files large enough to take advantage of these extra 2 GB of RAM, the RAM cache can speed performance of Photoshop.


If I understand this correctly, running CS2 on 64bit Windows XP will allow me to use up to 6GB of RAM. Photoshop will actually start using your excess RAM as a scratch disk before going to the HDD. Do you suppose if I had 8GB of RAM it would use that too? Or do you think it starts writing to the HDD after 6GB?

Either way, it might be wiser and cheaper to just buy another 2GB stick of RAM and let Photoshop figure out what to do with it. So if I'm not going to use the iRAM for a scratch disk, maybe I could use it as the windows page file? But again the guys at AnandTech don't seem to think it's worth it:

http://www.anandtech.com/storage/showdoc.aspx?i=2480&p=...
Quote:
The end result? There was no real tangible performance difference between putting more memory in the system and using the hard disk for the pagefile or putting less memory in the system and using the i-RAM for the pagefile. Granted, if we had a way of measuring the overall performance, it would have shown that we would be much better off with more memory in the system (it runs faster, and it is accessed much quicker than off the i-RAM).


I dunno what to decide. Maybe I should buy it anyway and run my own tests. I just can't seem to find enough consistent information about the iRAM.

Anyway.. whether or not I decide to go with the iRAM I still have to figure out the best way to arrange my hard drives for maximum performance. I have 8 SATA connections available, 4 of which I've already decided to use for my data disks. That leaves 4 connections left for my OS, page file and scratch disk. I really wanted to do RAID 0 Raptors for my OS, but then I would have to sacrifice page/scratch performance with only 2 connections left. Here are the options I've been looking at:

- 74GB RAID 0 Raptors for the OS and a single drive each for the page + scratch disks (they would have to be 7200s (4 Raptors is too much!))

- 74GB Raptor for the OS, 36GB Raptor for the Photoshop scratch disk, and RAID 0 20GB 7200s for the OS page file

- 74GB Raptor for the OS, 36GB Raptor for the OS page file, and RAID 0 40GB 7200s for the Photoshop scratch disk

Ultimately this is what I must decide... and this is why I was trying to establish how important the scratch drive is, how big it gets, and how often I will be writing to it.
February 20, 2007 8:53:31 PM

Yes, I believe that if you have 8GBs of RAM, Photoshop could take all of that in terms of scratch disk. Which is the most recommendable course of action.

Be careful with RAID 5 cause the reads are amazing but the writes are pretty bad.

What RAM are you going to buy? 2x2GB should not run you $600. I sent you some links for some good fast 4GB DDR2 800 RAM, are you considering FBDIMM for a Xeon rig? Or are you counting with Canadian dollars?

I will say it again, use your extra money for another 4GBs of RAM, or get a 2GB kit fo 6GBs. The choice is yours, but please put RAM above all else. If you get 2GBs only, that will leave you enough money to get 2x74GB Raptors in RAID 0 for the OS.

The recommendation by the guy to not use a scratch disk and just add more RAM is right on. I think you should max out your RAM first, and then see how your performance is going. If you dont think that 6GB or 8GB are enough, then think about the iRAM first, Raptor RAIDs second.

I sure hope you make a lot of money with your photoshop work. Id like to see that work sometime.
February 26, 2007 11:18:39 PM

Quote:
Yes, I believe that if you have 8GBs of RAM, Photoshop could take all of that in terms of scratch disk..


The Adobe quote contradicts that.

http://www.adobe.com/cfusion/knowledgebase/index.cfm?id...
Quote:
If you have more than 4 GB (to 6 GB (Windows) or 8 GB (Mac OS)), the RAM above 4 GB is used by the operating system as a cache for the Photoshop scratch disk data. Data that previously was written directly to the hard disk by Photoshop, is now cached in this high RAM before being written to the hard disk by the operating system. If you are working with files large enough to take advantage of these extra 2 GB of RAM, the RAM cache can speed performance of Photoshop.


On to other questions.

Quote:
Anyway.. whether or not I decide to go with the iRAM I still have to figure out the best way to arrange my hard drives for maximum performance. I have 8 SATA connections available, 4 of which I've already decided to use for my data disks. That leaves 4 connections left for my OS, page file and scratch disk. I really wanted to do RAID 0 Raptors for my OS, but then I would have to sacrifice page/scratch performance with only 2 connections left. Here are the options I've been looking at:

- 74GB RAID 0 Raptors for the OS and a single drive each for the page + scratch disks (they would have to be 7200s (4 Raptors is too much!))

- 74GB Raptor for the OS, 36GB Raptor for the Photoshop scratch disk, and RAID 0 20GB 7200s for the OS page file

- 74GB Raptor for the OS, 36GB Raptor for the OS page file, and RAID 0 40GB 7200s for the Photoshop scratch disk

Ultimately this is what I must decide... and this is why I was trying to establish how important the scratch drive is, how big it gets, and how often I will be writing to it.


I can help you with the Windows swap file part of your decision, if nothing else. Bottom line: I would put the Windows swap file (paging file, pagefile.sys) on a single large 7200 with a 16MB cache, with nothing else on the drive and no other drives on its controller. If you're interested, here is my reasoning, based on the Windows swap file having a lot of random access and not so much long, contiguous data transfer.

First, I would get a large drive because there is no waste of space: it is turned into performance through something called "short-stroking". (It is not just theory and anecdote; after much searching, I managed to find a test with results almost exactly as predicted, though I unfortunately did not bookmark it.) Hard drive manufacturers have to keep average seek times down as they increase disk sizes in order to maintain expected performance. A disk that is twice as large with the same average seek time over its total range must seek twice as fast per GB on average. Since a Windows swap file is of limited size -- I use the "RAM plus 1GB" rule of thumb for it, so I would use 7GB in your shoes -- then I would expect a disk that is twice as large (with the same average seek time over the total disk) to jump around in the swap file in half the time. Also, I wouldn't bother getting a Raptor for it because I would doubt that it would benefit much from faster continuous transfers. In plumbing analogy, it matters more whether this pipe is short than whether it is wide.

I would put it on its own dedicated drive controller as well as on its own drive because I read about a test (also not bookmarked, sorry) that found a significant (though less than 10% IIRC) benefit to overall system performance from that. Oddly, the test did not find much benefit to overall system performance just from having it on its own physical disk sharing a controller. I don't fully understand how having its own controller helps -- something to do with the controller already pointing at the correct place for most seeks? -- but I'm an "evidence over all" kind of guy so I'm going with it.

I would not bother putting it on any kind of RAID array because, with that much RAM, Windows would just be using the swap file for kicks and giggles anyway.

Here is where I enter into pure speculation, not backed up by tests. I'm skeptical that the OS would benefit much from being on a Raptor instead of a short-stroked 7200 on a dedicated controller. (Does it really do that much reading of large files compared with random access?) However, it's possible (probable?) that the Photoshop swap file would benefit from a Raptor, given your expected file sizes.

Finally, if your choice of four disk RAID 5 was a more casual decision and your data is important to you then I would suggest taking a closer look at its suitability for your primary intended use. I would specifically look at the vulnerability of RAID 5 to things like controller failure and compare its overall fit for your purpose with RAID 1 with two disks on independent controllers.
March 1, 2007 8:15:35 PM

Sorry, Scientivore. I haven't visited this thread for a while, I didn't mean to leave you're thoughtful reply hanging there.

Thanks for your suggestions, I will take them into consideration. Your idea of using a short-stroked 7200 for the swap file is interesting. I assume you are suggesting that I get an 80GB or 120GB drive and partition just the outer edge as the swap file? This makes sense to me.

As for the RAID setup, I am still researching the best arrangement. It seems to be a never-ending series of conflicting benchmarks and opinions. :roll: But I am narrowing down a few options... which I can explain sometime in another thread in Homebuilt.

Cheers.

Art.
March 3, 2007 1:17:09 AM

Quote:
I assume you are suggesting that I get an 80GB or 120GB drive and partition just the outer edge as the swap file?


Yes, exactly. No need to spend a lot of dough on it since it probably won't be used much anyway, and bigger is better (all else being equal).

Quote:
As for the RAID setup, I am still researching the best arrangement. It seems to be a never-ending series of conflicting benchmarks and opinions. :roll: But I am narrowing down a few options... which I can explain sometime in another thread in Homebuilt.


I'd be interested in reading that thread since I'm about to dive into digital photography and artistic photomanipulation. So, I fear that I may soon discover a need for faster data stores. ;) 
Anonymous
a b G Storage
May 31, 2009 10:48:02 PM

The answer to your question "how much scratch disk space can Photoshop use?" is... as much as Photoshop needs. It says on Adobe's site that a PS file can need around 10X its physical size in memory to execute filters, save history and so forth. So it follows that if you working on a 600MB PS file, Photoshop can require upto 6GB of memory. This will first be assign to RAM and then scratch disks. The scratch disk is used as a virtual memory.
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