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atort13@mac.com
02-03-2007, 01:50 PM
Ok, I hear different things all over the place regarding the reasonable amount of scatch disk space to allocate to a specific drive. My scenerio....A new dual 3 MacPro with 4 gigs of RAM and two of the four bays filled with 750 gig drives. I partitioned the second drive with 100 gig scratch disk after running the same basic configuration for years with a 30 gig scratch. I figure since I have so much drive space lately I would allocate more, but some tell me that 100 is a safe number and others say with 4 gigs of RAM I will never touch that amount. I shoot with a camera that throws out 22mp files and the are big, but never much more than a gig. Should I not waste the space and just allocate 30 or 50 gigs, keep it where it is at being 100, or ??? With 4 gigs of memory will I really be running out of disk? I hear that the basic formula for scratch disk allocation is roughly 5 times the amount of RAM in the computer, which would mean even 30 gigs would be more than enough with 4 gigs. Any info or input is appreciated. Thanks!

TZ
02-03-2007, 02:00 PM
After reading the Photoshop Acceleration pdf Guide, and downloading the Photoshop Test Utility, you will have some idea of how your system handles your files and needs.

I don't think the 750GB Barracuda is what you want for scratch.
You might want to create and boot from a RAID.
Has Barefeats been one of your stops along the way for ideas?
If you have or can afford a couple drives, I'd investigate the 10K Raptors.
RAM prices have dropped for Mac Pro making a 2GB kit from Crucial $359 now. So if you are dealing with 1GB size files, and for today, CS2 runs under Rosetta, I'd say 4GB is minimum RAM.

How bad is it now? how much better do you need? or do you just want to confirm whether your current setup is "good enough" if not ideal?

A 10K Raptor boot drive helps some. 2GB RAM more helps some. A 10K Raptor for scratch (85MB/sec writes, the 7200.10s have some issues with write performance in non-RAID setup still). So you could gradually upgrade and add and cut times down some.

There are test results a couple threads down in this forum.

atort13@mac.com
02-03-2007, 02:11 PM
I partitioned the 750GB Barracuda and hear from shooters who have been the very first on board in Chicago at least shooting digitally and doing things this way and say that it is definitely quicker to have an internal drive as a scratch disk as opposed to anything external. These people should know something and a few have big dollar $17k XRaids and could easily do something slick and say it is not quicker or needed. Ahhh, I am confused;) Others I know who are just very techy say 4 gigs of RAM is huge even with the files I am working with. How do you figure or say 4GB is minimum RAM? Just curious to why you say that and you think 6GB or 8 GB would really be needed? Thanks. Anthony

TZ
02-03-2007, 02:36 PM
OS X uses your RAM for cache and scratch first, and only then will it hit your disk drives.

Please... read the pdf and look at Boots test and article.

4GB is not "huge" in today's world. Not on Mac Pro and Tiger. Not with Vista, and not for CS2. A Mac Pro needs a minimum of 1.5GB RAM + memory for Rosetta along with 3.5GB for now for CS2. Then throw in free memory for virtual scratch/cache volume.

Scratch disks use to be external 15K SCSI RAIDs. Today, the focus is on raw cpu and memory, and only then on scratch.

I would rather build a smaller two drive boot RAID that is also used for scratch, and have 6GB or more of RAM - but read the benchmark results and use the test program.

Boots
02-04-2007, 07:57 AM
I partitioned the 750GB Barracuda and hear from shooters who have been the very first on board in Chicago at least shooting digitally and doing things this way and say that it is definitely quicker to have an internal drive as a scratch disk as opposed to anything external. These people should know something and a few have big dollar $17k XRaids and could easily do something slick and say it is not quicker or needed. Ahhh, I am confused;) Others I know who are just very techy say 4 gigs of RAM is huge even with the files I am working with. How do you figure or say 4GB is minimum RAM? Just curious to why you say that and you think 6GB or 8 GB would really be needed? Thanks. Anthony

Hi Anthony,
Welcome to the forums if someone has not already done so!

Coming up with an exact calculation for a suitable scratch volume size has always been difficult- there are a bunch of variables to account for, such as installed RAM, image size, number of History states, number of Save states in History options- and of course how big your images grow with layers and channels. Adobe has a method here (http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=320005) for guesstimating.

100GB is certainly safe for what you've described thus far; 50GB or even 25GB might be just fine. How big do the images become? How much History? It's really up to you to take a close look at your workflow, and determine your maximum scratch file sizes.

You could test this out by setting your scratch to a big volume, set your History to about how many operations you would typically perform on an image, open a typical image, run through everything- and then look at the size of the scratch file in the Finder before closing the image. What about scanning? Any big scans? 16bit images?

With your 1GB files, and 4GB installed RAM, you will be hitting the scratch disk on a regular basis.

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Unfortunately, with Mac Pro, we're still waiting on a Universal Binary version of Photoshop, so we have to use Rosetta to run CS2, and Rosetta wants 1-2GB RAM for itself.

As far as Photoshop is concerned, Mac OS 10.4 is a 64bit operating system. Even though Photoshop is still a 32bit application, it takes advantage of this by telling the OS to use extra RAM above 4GB installed as a cache for scratch disk data. When you have more than 4GB RAM installed in the machine, and you work with big files such as your 1GB files, this caching of scratch data in RAM speeds up performance. With big files, the more RAM you add, the more significant the improvement.

If you have other applications like Bridge open at the same time, you need even more available memory. If you want to take advantage of Photoshop caching scratch data, you need a minimum of more than 4GB RAM. Rosetta wants 1-2GB for itself...

So that's 4+2+: at least 6GB installed RAM to run Photoshop optimally when big files like yours are in play. 8GB would be even better.

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Fast scratch disks: if you work with really large files, a really fast dedicated scratch disk will improve performance. 4-6 15k SCSI or SAS drives in a RAID0 is pretty much the fastest affordable setup- the most the system can really use before diminishing returns (for Photoshop) take a steep dive.

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To echo TZ-
I would say, for your situation as described- consider adding more RAM first. It will be even more beneficial in the long run- especially when CS3 arrives (assuming you upgrade).

Yes, if you installed a couple of Raptors for scratch, you'd also get a bump- but not as much as from installing more RAM. If anything, I'd be more likely to consider a Raptor- or striped pair- as the startup disk, then use one of the big 750GB as your image bank...