Photoshop (as well as other high-end graphic and video production software) is a heavy user of hard drive access. The speed of the hard drive in a machine and the way that hard drive use is organized can have a major impact in performance, especially with large files. Photoshop makes extensive use of Scratch disk files, which are temporary files that are continually created, read and changed as you work on images. Scratch files are part of Photoshop’s virtual memory management.
This is separate from the Swap or Virtual Memory files that the operating system (Windows or OSX) uses for itself. The more RAM memory you have, the less the OS has to hit its Swap files for data, which is good, because RAM is many times faster than a hard drive. Another thing that is important – make sure you are running a 64-bit operating system and a 64-bit compatible version of Photoshop, so that Photoshop can access all the memory it can – under 32 bit operation it is limited to 2.1 – 3.0 GB (Mac 32 bit) or 1.7 – 3.2 GB (Windows 32 bit) of application memory.
To repeat, running 64-bit and getting as much RAM as you can afford – up to about 12 GB – is the most important step. Above 12 GB, more RAM can still help but the marginal benefit declines. So – on to hard drives:
There are two technologies that speed up disk access, RAID striping (using two interleaved drives as one drive for faster access) and SSD (Solid State Drive, which can be much faster to access than a rotating hard drive). Setting up a SSD as a boot drive for the computer is a popular hobbyist upgrade. It will make booting times faster, which is enjoyable, but may be a bit of a waste for Photoshop. Here’s why:
The key with Photoshop is to put the different hard drive functions on different drives. Instead of spending money RAIDing hard drives or installing an ultra-fast boot drive, first install separate drives for Boot drive, Data drive and Scratch drive.
Why? Because we want to eliminate contention for control of the drive head. The worst case scenario is to have everything on one hard drive – Imagine, as Photoshop is dealing with a data file, wait, the OS has to take over the drive to write a Swap file. This causes a delay as the drive head is swung over to the swap file area. Wait, now Photoshop has to read from its Scratch – another delay to reposition the head. Wait, now Photoshop has to read some program code to run a filter, but wait, first it has to write some changes to the data file… you see how the delays add up as one drive read/write head has to be cook, waiter, cashier and dishwasher all at once.
By splitting up the tasks among multiple drives, each of the drive heads can stay on-task and be reading, writing and repositioning efficiently without interruption from other duties.
Your scratch drive should be your fastest drive and it should have nothing on it but the scratch space for Photoshop (and NOT the Windows swap file). Since the scratch function only needs a few 10’s of GB, you can partition the drive, give the first (fastest) partition to scratch, and you can use the 2nd partition for backing up your system or data.
Then, get your Photoshop data files off of the boot drive. Data should be on a drive by itself. A large, high speed hard drive like a Western Digital Caviar Black drive is a good choice here.
So far you have three drives – your original Boot drive, your Scratch drive and your Data drive. If you want a bit more speed, you could also create a dedicated drive for the Windows swap file, or move the program files off your Windows drive. These will help a bit but are not essential.
Once you have divided the tasks between different drives, then you can think of RAID or SSD to further speed it up. Personally, I think a SSD makes more sense as a scratch drive than a boot drive, because you boot only once per day, but scratch is constantly writing small files – where the close to zero latency of the SSD will help – and SSDs are generally smaller in capacity, which is fine for a scratch drive. A downside of using a SSD as a scratch is that you might wear it out – SSD flash memory is only good for a limited number of writes. Granted, that limit is in the millions, but constant use as a Scratch drive may wear it out in a couple or three years. Think of it as an investment, plan to spend $200 every three years on a new Scratch drive.
Then if you still want to RAID, create a RAID 0 Striped array on the Data volume, where you are reading and writing very large files, and the increased sustained throughput will win. The larger a file is, the less important the initial rotational latency is and the more important that sustained throughput is.
But if you do set up a RAID 0, you -must- have a rock solid backup regimen, because you have increased the risk of failure. If one of the two striped RAID drives has a problem, you lose ALL of the data on both drives.
Adobe: Assigning scratch drives http://help.adobe.com/en_US/photoshop/cs/using/WSfd1234e1c4b69f30ea53e41001031ab64-748aa.html
Performance optimization: http://kb2.adobe.com/cps/404/kb404439.html
This all makes sense for a MacPro or a Windows tower machine, where you have multiple drive bays to play with, and you can install an eSATA card for high speed external drives. If you have a Windows laptop, an iMac or a MacBook Pro, your options are more limited. If you want to run with the big dogs, you need the MacPro or a tower PC.
If you are working with a notebook, an iMac or MacBook Pro the USB 2.0 interface is just not up to the task of handling a scratch drive or a fast data drive. Firewire 800 is faster, but you will lose a step or two compared with the SATA drives. Some models of Windows notebook, the 17″ MacBook Pro and earlier models of 15″ MacBook Pro have ExpressCard/34 slots, which you can get an eSATA interface for. This is faster than Firewire 800, but a little finicky. There is great promise with the new Thunderbolt interface on the latest MacBook Pro and iMac models, with SATA level speeds available to hard drives once products start shipping. I can see a Thunderbolt SSD scratch drive being a popular item.