Scratch Disk?

[Bonito]

Can someone please explain to me what a scratch disk is and how it
is used. Mac platform here. I thought I had heard you could use
an external hard drive for a scratch disk for photoshop - is that true?
If so, does it slow down things? Very confused. :rolleyes:

[MaxxuM]

Scratch disk simply means a place photoshop will use as temporary or virtual memory. The faster the drive the better, so using an external drive as the swap is not really optimal unless you're doing constant writes like in video.

[CyberDyneSystems]

As Maxxum says, speed is best.

SSD: Your best options for a scratch disk is small and fast..
right now the optimal choice would be a fast SSD (solid state drive) in the 32GB - 64GB range.
A little esoteric, but seriously they are the perfect choice for anyone seriously interested in a dedicated scratch disk. And if you only get a slow separate scratch disk, you may as well not bother.

The same SSD option would also be perfect for a Windows swap file,. (the OS level version of Photoshop's "scratch disk" )
I don;t know if Mac OS uses a swap file too, but I would asume so, and hopeful it to can be moved to such a disk.

External:
Usually external is a bad idea when speed is of utmost importance like in this case,
However if your Mac supports E-Sata, you get the same speeds as your internal drives.

[Quad]

SSD makes for a poor scratch disk. It has better read than write performance as a write must do a wipe then write and scratch likes write performance. Low latency is good as well. I use ssd's so I know what speed they are capable of (they make great install and data disks when data is read more than written to).

Here are you fastest to slowest scratch options (based upon what I have used)

1) iRAM (I have used two and if 4 or 8 gb will do and especially is you have some old memory laying about this is the best). There is no error correction and this has caused me problems.

2) Raptor - fast and low latency (I have not tried 15K SAS but it should be even better)

3) a fast drive (I like Caviar Black 640 and up) short stroked (make a partition of the first third and use that).


RAID 0 best (3 drives seem to top out), hardware RAID controller better than software but in RAID 0 mostly for the onboard cache. A separate controller is the next best thing, a separate drive next.


Look at your scratch file when you are in the heat of a big edit and you will see how big it is then you have an idea of how big you need.

When I used the iRAMs and the scratch file had to go to a regular harddrive it was coffee time as far as computer performance was concerned. Photoshop loves memory and my machine has 12 GB and I still hit the scratch disk lots. When it hits the scratch file gets big fast as well so it must dump more than just what it needs for file to fit in memory.

Again this is just what I have experienced I am sure others have gotten different results. I am fortunate in that I get lots of performance hardware given to me so I can try lots of different things.

[CyberDyneSystems]

Quad, have you used a latest Gen SSD?

Even in the last few months there are models who's speed is much faster in writes and latency.
Up 170MB/S writes.. 250 MB/s reads.
Are you saying that even these drives drop that much in speed?

Raptor is another great choice for dedicated Scratch.. I usually mention them too.

The I-Ram rocks, but is standing still in performance. still hampered by Sata 150 speeds and the cost of old DDR and no way to get over 4GB on a single card. It's just not an easy option for most people. what I'd give for a DDR2/SATA 3G version! Especially one that used SATA power instead of a PCI slot!!!

Still, I have an I-Ram in my machine, at the time SSD was too slow and costly to consider.

[DeCeccoNET]

Am I the only one who is uncomfortable recieving technology advice from somthing that will one day become Skynet and send Terminators to kill us all? :cool:

[CyberDyneSystems]

........... SSD = Easier and faster for SkyNet to overwrite and drop it's A.I. on..
...and less susceptible to G-Shock when it stands up and walks away... :mrgreen:

[Bobster]

go for say 24GB RAM, give PS 8 GB, make a RAM Disk of 12, and let the OS have the rest :)

use the RAM Disk as Scratch :D

[CyberDyneSystems]

I don't think there is a Mac version of PS that can use 8GB of RAM, but I agree with the virtual ramdrive.. I use that too :)

[Bobster]

oh right, yeah i keep forgetting, Mac Users have to wait a whole nother release until they get 64bit support..

[Rodinal]

oh right, yeah i keep forgetting, Mac Users have to wait a whole nother release until they get 64bit support..

I don't think we'll ever get it.
CS4 on OS X is fast as it is, no need for 64-bit :) Seriously, guys. My raw files don't exceed 10 mb. What are those from the 5DII ? Something like 20 mb? So where's the need for 64-bit? I imagine for those who own a gazillion-pixel medium format back. For various reasons 64-bit does make a difference even on smaller files on Win. It won't on Mac, unless you play with really huge files.

[Quad]

Quad, have you used a latest Gen SSD?

Even in the last few months there are models who's speed is much faster in writes and latency.
Up 170MB/S writes.. 250 MB/s reads.
Are you saying that even these drives drop that much in speed?

Raptor is another great choice for dedicated Scratch.. I usually mention them too.

The I-Ram rocks, but is standing still in performance. still hampered by Sata 150 speeds and the cost of old DDR and no way to get over 4GB on a single card. It's just not an easy option for most people. what I'd give for a DDR2/SATA 3G version! Especially one that used SATA power instead of a PCI slot!!!

Still, I have an I-Ram in my machine, at the time SSD was too slow and costly to consider.


True not the latest ones my drives are already about 6 months old already. Positively ancient for cutting edge tech. I see the latest Intel X25-E drives have really jacked up the write speeds. My drives get about 210mb/sec reads, writes in practice are about half that. I just have not been that crazy in love with them as scratch disks. Latency is great though and that is very important for a scratch disk. It could be that other things are holding me back so it keeps the scratch disk from shinning like it should.

I have been using 2 Raptors but am thinking of asking for some SAS 15Ks to try out (I usually get to ask for some crazy stuff in the fall and then it one day appears on my desk and no one asks for it back).

I don't mind the old memory in iRAM because often it can be found for free as no one want to put it in a computer anymore. Often large institutions have sales where they sell stuff from labs and such for pennies to get rid of it. You just need to have an inside source telling you when the sales happen. I have bought things from universities like language lab tape recorders for a quarter. A great toy for a kid BTW with the tape speed dial. Old memory can usually be found. Still a SATA-2 16 gig model that goes into a CD ROM sized box would be great. Gigabyte made one like that but only 4 GB & SATA and I never saw it for sale. It's time is now past.

[Bobster]

I don't think we'll ever get it.
CS4 on OS X is fast as it is, no need for 64-bit :) Seriously, guys. My raw files don't exceed 10 mb. What are those from the 5DII ? Something like 20 mb? So where's the need for 64-bit? I imagine for those who own a gazillion-pixel medium format back. For various reasons 64-bit does make a difference even on smaller files on Win. It won't on Mac, unless you play with really huge files.
I end up with 1.5-4GB PSB files, so having the ability to have more RAM in my machine is very useful.. its probably why I end up with the editing work I do, because the Mac can't hack those kind of files..

you say sure the RAW is 10MB, but then when you process it as a 16bit 30x20in file, add a few layers, boom! your file is huge! :)

64bit is wasted on those people who use small files, its more a bragging right than usefulness..

remember the way PS works is you take your original file size and multiply it by five to get the real amount of physical RAM needed to work at 100% efficiency.. once you start adding layers, everything increases!

[In2Photos]

64bit is wasted on those people who use small files, its more a bragging right than usefulness..

For those not working on large files they may as well be using Elements as it likely has enough tools to do what they need anyway.

[Tony-S]

I don't think there is a Mac version of PS that can use 8GB of RAM, but I agree with the virtual ramdrive.. I use that too :)

OS X (since 10.4.11) uses excess RAM as a cache, so while PSCS4 can only address ~3.2 gb, the scratch disk will be in the available RAM until it fills, then spill over to the secondary device (e.g., hard drive, ssd, etc.).

For 99% of Photoshop users, I suspect 32 bit is more than adequate. The largest PS document I have is about 900 mb opened (a 5Dii HDR photomerged pano).

[Quad]

At one time no one need full frame DSLR cameras (esp. according to Nikon) yet there are many people (obviously delusional) who seems to buy them.

People have often told me that I will not possibly use the memory I figure I will need in a new machine and yet I seem to use it and still end up with 60GB scratch files. Working non destructively does add lots of bulk to files and as more and more aspects of photo editing go the non-destructive route memory demands will keep increasing and with that the need for fast scratch disks.

How much memory will be needed for non-destructive 32 bit edits? A large number I expect and people will now say that will never be needed as they often do before the technology makes it possible. Once it becomes possible users will find a use for it.

[CyberDyneSystems]

OS X (since 10.4.11) uses excess RAM as a cache, so while PSCS4 can only address ~3.2 gb, the scratch disk will be in the available RAM until it fills, then spill over to the secondary device (e.g., hard drive, ssd, etc.).
.

The same work around I've been using for years running 8GB RAM on a 64 bit OS with a 32 bit PS,.. . just automatically done by the OS,. nice :)

[Moppie]

OS X (since 10.4.11) uses excess RAM as a cache, so while PSCS4 can only address ~3.2 gb, the scratch disk will be in the available RAM until it fills, then spill over to the secondary device (e.g., hard drive, ssd, etc.).




How does PS know to use the extra RAM for it's scratch disk?
Or is this something that OS-X behind the scenes?

[Bobster]

How does PS know to use the extra RAM for it's scratch disk?
Or is this something that OS-X behind the scenes?
its the same for CS3 on XP64 or Vista64, anything over 3.5GB and it uses it as scratch..

[Tony-S]

How does PS know to use the extra RAM for it's scratch disk?
Or is this something that OS-X behind the scenes?

I don't know the details but I read it on an Adobe tech note on their web page. Depending on the OP's Mac, she may be better off maxing her RAM.

[Moppie]

its the same for CS3 on XP64 or Vista64, anything over 3.5GB and it uses it as scratch..

I don't know the details but I read it on an Adobe tech note on their web page. Depending on the OP's Mac, she may be better off maxing her RAM.


So what happens if you set a disk to be used as scratch in photoshop?
Will it ignore that, and use the extra RAM first?

[Tony-S]

The disk is used second, cache first.

[Moppie]

The disk is used second, cache first.

Cool.

I know someone with a Mac Pro, and 6GB of ram who was having issues with very large files. I'll let him know. :cool:

[Tony-S]

Have a read here (http://kb2.adobe.com/cps/404/kb404440.html) - in case I misunderstood anything...

Edit: Where it starts "Allocating Memory with 64-bit Processors".

[Bobster]

Cool.

I know someone with a Mac Pro, and 6GB of ram who was having issues with very large files. I'll let him know. :cool:
that's not going to help with the lack of RAM in Photoshop department.. it doesn't matter how much scratch you have, if something can't be done in RAM then you'll still get the out of Memory error..