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Author Topic: IS a dedicated scratch disc needed?  (Read 999 times)

mdijb

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IS a dedicated scratch disc needed?
« on: March 09, 2017, 06:59:56 PM »

I am using a 2009 MAc Pro with Photoshop CC 2017, and am considering upgrading my machine with an SSD , a new video card with #gb of RAM, and adding RAm to total 32 GB from the folks at OWC.

My current config uses a dedicated, 10,000rpm hard drive as a scratch disc.

If i upgraded my machine with  the above, do I even need a dedicated scratch, or is the added Ram enough to give better performance?

I will post this on the Computer forum as well.

MDIJB
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TonyW

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Re: IS a dedicated scratch disc needed?
« Reply #1 on: March 10, 2017, 05:22:53 AM »

Unless PS CC 2017 has changed since earlier versions it will write to scratch disk regardless of the amount of memory.  Of course it may not need to read from scratch due to the memory amount.

I can only theorise here but I would suggest as you already have it leave your scratch disk to take the PS write hits. 

Your PS speed should now be solely reliant on your CPU, GPU and memory speed limits
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E.J. Peiker

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Re: IS a dedicated scratch disc needed?
« Reply #2 on: March 10, 2017, 09:02:40 AM »

I am using a 2009 MAc Pro with Photoshop CC 2017, and am considering upgrading my machine with an SSD , a new video card with #gb of RAM, and adding RAm to total 32 GB from the folks at OWC.

My current config uses a dedicated, 10,000rpm hard drive as a scratch disc.

If i upgraded my machine with  the above, do I even need a dedicated scratch, or is the added Ram enough to give better performance?

I will post this on the Computer forum as well.

MDIJB

Is it a requirement to have a dedicated scratch disk?  No, it never was
Will one improve performance?  Maybe, depends on the hardware
Will an non-dedicated SSD based scratch be faster than a dedicated HD? probably, depends a lot on the SSD.
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kers

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Re: IS a dedicated scratch disc needed?
« Reply #3 on: March 10, 2017, 10:10:39 AM »

I have noticed that it helps to choose your scratch disk to be the fastest disk you have with enough room on it.
I do not think you need a special dedicated disk.

As mentioned the disk will always be used no matter how much ram, but the amount depends on your type of use.
With 32 gig ram you will be able to get along with 256GB unused space on the scratch disk even with very big files.
( then i think of 10GB files)

« Last Edit: March 11, 2017, 06:49:48 AM by kers »
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scyth

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Re: IS a dedicated scratch disc needed?
« Reply #4 on: March 10, 2017, 02:43:06 PM »

Unless PS CC 2017 has changed since earlier versions it will write to scratch disk regardless of the amount of memory.

it does... I have a notebook with 32Gb RAM... I put 8Gb to RAM disk (where all kind of temp files go, from browsers, etc, etc) and set PS to use this RAM disk first, then SSD drive
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TonyW

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Re: IS a dedicated scratch disc needed?
« Reply #5 on: March 10, 2017, 04:05:47 PM »

it does... I have a notebook with 32Gb RAM... I put 8Gb to RAM disk (where all kind of temp files go, from browsers, etc, etc) and set PS to use this RAM disk first, then SSD drive
Interesting but I am pretty sure that you could if you wanted use a RAM disk as another Scratch Disk in earlier versions of PS too, after all a properly configured RAM disk should be seen by the system as another disk device.

As I have not done any recent testing I wonder if you have run any tests to compare to see if you are getting a worthwhile improvement (Photoshop only).  Particularly if taking away 25% of your 32GB RAM resources and turning it into an 8GB Ramdisk offers worthwhile benefits over just allocating the maximum RAM you can in PS in the first instance?

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scyth

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Re: IS a dedicated scratch disc needed?
« Reply #6 on: March 10, 2017, 04:44:09 PM »

Interesting but I am pretty sure that you could if you wanted use a RAM disk as another Scratch Disk in earlier versions of PS too, after all a properly configured RAM disk should be seen by the system as another disk device.

As I have not done any recent testing I wonder if you have run any tests to compare to see if you are getting a worthwhile improvement (Photoshop only).  Particularly if taking away 25% of your 32GB RAM resources and turning it into an 8GB Ramdisk offers worthwhile benefits over just allocating the maximum RAM you can in PS in the first instance?

my raws are small = just 42mp and I do not do a lot of layers in PS or some stitching/stacking ... so in my case 8Gb from RAM to RAM disk ( http://www.ltr-data.se/opencode.html/#ImDisk ) do not do any harm, plus again all other temp files from a lot of other software go there too instead of SSD... and RAM disk has 10+ times more throughput even vs PCIe SSD (and 100+ vs any SATA SSD)
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TonyW

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Re: IS a dedicated scratch disc needed?
« Reply #7 on: March 10, 2017, 04:49:39 PM »

my raws are small = just 42mp and I do not do a lot of layers in PS or some stitching/stacking ... so in my case 8Gb from RAM to RAM disk ( http://www.ltr-data.se/opencode.html/#ImDisk ) do not do any harm, plus again all other temp files from a lot of other software go there too instead of SSD... and RAM disk has 10+ times more throughput even vs PCIe SSD (and 100+ vs any SATA SSD)
Thanks, and yes I can see the speed advantages over any disk including SSD and it certainly can be useful fir other apps
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scyth

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Re: IS a dedicated scratch disc needed?
« Reply #8 on: March 10, 2017, 05:39:47 PM »

Thanks, and yes I can see the speed advantages over any disk including SSD and it certainly can be useful fir other apps

one note though - once W10 wants to do a big update redirection of TMP/TEMP folders to RAM disk shall be disabled till update/reboot completed... because RAM disk (w/ that particular software) is initialized later in the W10 loading process, at least it was my experience.
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mdijb

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Re: IS a dedicated scratch disc needed?
« Reply #9 on: March 11, 2017, 05:51:48 PM »

I looked up Ram Discs and think this might be worthwhile.  However if I am using SSD and 32 GB of Ram or more, is a ram disc serving as a Scratch disc even necessary--IS this unneeded duplication?
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TonyW

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Re: IS a dedicated scratch disc needed?
« Reply #10 on: March 11, 2017, 06:34:17 PM »

I looked up Ram Discs and think this might be worthwhile.  However if I am using SSD and 32 GB of Ram or more, is a ram disc serving as a Scratch disc even necessary--IS this unneeded duplication?
Regardless if what you may think you need PS will setup a scratch disk - so Adobe seems to deem it necessary. 

Default is the same drive as your OS which is not usually the best choice. 

A RAM disk is going to be the fastest you can get for both read and write, but you are going to loose a portion of your memory for the disk.

In your situation as you have an existing scratch disk why not re utilise it in your new setup and leave all the RAM for application use? 

While I am fairly sure that PS will write to scratch regardless of memory amount (if nothing else the history states) the key seems to be that it will not need to read until it runs out of RAM memory which in your case may be rarely/ never due to amount of RAM

Just keep an eye on efficiency status if it is regularly falling below 100% then the scratch will be being used and PS will be slower, once it falls below 80% you will likely notice loss of performance.  Lower than this and it will be very lethargic

This is what Adobe say about optomising
https://helpx.adobe.com/photoshop/kb/optimize-photoshop-cc-performance.html
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razrblck

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Re: IS a dedicated scratch disc needed?
« Reply #11 on: March 12, 2017, 06:31:49 AM »

It's useful for really large files, there's always some stuff written to disk even if you have enormous amounts of memory. I think PS also writes the auto save files there. The faster it is the better, I have a shared SSD for it but on my next workstation I will use a dedicated SSD for that (and other applications too, PS isn't the only one needing scratch disks).

It's not necessary, but it is useful when you work on large files with many layers. I have noticed a big speed boost in such conditions compared to a mechanical drive.
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scyth

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Re: IS a dedicated scratch disc needed?
« Reply #12 on: March 12, 2017, 12:56:51 PM »

I looked up Ram Discs and think this might be worthwhile.  However if I am using SSD and 32 GB of Ram or more, is a ram disc serving as a Scratch disc even necessary--IS this unneeded duplication?

if your workload is RAM limited (not my case) then you certainly want all RAM available for apps, otherwise (my case) I prefer not to put a lot of unnecessary writes (again - not only from PS) to SSD
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tom b

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Re: IS a dedicated scratch disc needed?
« Reply #13 on: March 12, 2017, 01:35:10 PM »

IS a dedicated scratch disc needed?

Probably 15 years ago yes, today no. Moore's Law has shown that we have enough computer power.

Cheers,

Simon Garrett

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Re: IS a dedicated scratch disc needed?
« Reply #14 on: March 13, 2017, 04:56:57 AM »

IS a dedicated scratch disc needed?

Probably 15 years ago yes, today no. Moore's Law has shown that we have enough computer power.

Cheers,

I'm not sure it's a matter of Moore's Law.

The issue is to get fast access to the scratch disk.  With mechanical hard drives, speed of access is determined by drive throughput and drive seek time.  If other applications (or Windows) are using the same drive, then when Photoshop wants the scratch drive the head may have been moved to another file somewhere else on the disk, so seek times are higher.  With an SSD, seek times are approximately zero, so it doesn't matter so much if something else is using the same drive.  There is just the matter of throughput, and of course if other applications are using the same drive there could be contention for that throughput, but this is a smaller issue than seek times.

The drives with the fastest throughput are NVMe SSD drives.  These use PCIe rather than SATA interfaces, so have a potential throughput of up to 32Gbs rather than SATA's maximum of 6Gbs.  Typical NVMe SSDs have a throughput of 20-30Gbps.  The best solution is probably to have an NVMe SSD C drive, which can also be the Photoshop Scratch drive.  There's probably little advantage in a separate Photoshop scratch drive, so long as the C drive is an NVMe SSD. 

Most NVMe drives have a so-called "M.2" socket interface, and modern motherboards usually have one or two M.2 sockets.  If not, one can get PCIe adaptor cards with an M.2 socket on them, on which one can mount an NVMe SSD drive. 
« Last Edit: March 13, 2017, 09:37:48 AM by Simon Garrett »
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DottieC

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Re: IS a dedicated scratch disc needed?
« Reply #15 on: March 16, 2017, 09:48:01 AM »

You probably know this but the early 2009 Mac Pro cannot be updated to Sierra. I have an early 2009 Mac Pro which I was thinking of refurbishing pretty much the way you are, but gave up on it when I realized that the newest Mac Operating system would not run on it. Once you get behind on the operating systems it is not that far off before updated Adobe products like Lightroom and Photoshop don't run on it. The later 2009 MacPros can be upgrade to Sierra.

http://www.apple.com/macos/how-to-upgrade/#hardware-requirements

I am saving my money towards a newer machine in a few years. Will a new Mac Pro ever come out?

good luck.
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Jim Kasson

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Does a scratch disk affect response on high-RAM machines?
« Reply #16 on: March 16, 2017, 12:41:46 PM »

On my computer, it does not seem to. I changed my Ps scratch disk to a moderately slow USB3 mirrored external drive. I built 4 and 5 GB images and manipulated them, while watching the drive activity lights on the scratch disk. As others have said, even though PS had plenty of RAM, Ps used the scratch disk from time to time. However, I never saw it use the scratch disk during any operation long enough to cause Lr to throw up the progress bar for more than a second or two. When the operation took a minute or do, the scratch disk light never came on.

My tentative conclusion is that, if you've got enough RAM, it doesn't matter what setting you use for your scratch disk; your response times will be the same.

Machine configuration:

2 Xeon 12-core processors
AMD FirePro W8100
256GB RAM
Windows 10 Pro

Could others do similar tests and see what they find?

Jim

TonyW

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Re: Does a scratch disk affect response on high-RAM machines?
« Reply #17 on: March 18, 2017, 01:29:19 PM »

.....
My tentative conclusion is that, if you've got enough RAM, it doesn't matter what setting you use for your scratch disk; your response times will be the same.

Machine configuration:

2 Xeon 12-core processors
AMD FirePro W8100
256GB RAM
Windows 10 Pro

Could others do similar tests and see what they find?

Jim
Hi Jim,
Your tentative conclusion pretty much agrees with my own thoughts and experience with PS including CS6 and CC.  As you say with enough RAM (or more than enough for that matter) for the job in hand PS will always write to scratch disk either one you have configured or the default drive being the same as OS.  But it will not need to access the drive as long as memory sufficient and therefore a slow drive really should not affect performance - unless the image requirements exceed memory.  In that case I suspect that the slow down may be much more painful than would be experienced with a fast HDD or SSD, due to needing to access the data written to the drive

With a slow system with low memory the scenario seems to be very different depending on what is being worked on.  It seems to me that once below 80% efficiency PS slow down apparent most often as long as efficiency stays down. 

Mind you with your heroic system 2x Xeon and 256GB RAM  8) I would imagine it would take some very heavy lifting before it even noticed there was a load being applied  :D

My own Windows 10 system pales in comparison to yours being single i7 processor with at present only 16GB RAM.  Scratch disk being allocated to second drive HDD rather than SSD used for OS and applications such as PS.  I have not seen or noticed any performance issues or slow downs so far.  Having said that I have not been working on 4-5GB images - yet!

Bear in mind that my view is subjective and I have not tried to run any tests to confirm
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rdonson

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Re: Does a scratch disk affect response on high-RAM machines?
« Reply #18 on: March 18, 2017, 04:38:01 PM »


Machine configuration:

2 Xeon 12-core processors
AMD FirePro W8100
256GB RAM
Windows 10 Pro

Jim

Jim, I think you're pretty much an outlier with 256GB RAM in your machine. 
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Regards,
Ron
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