Adobe Photoshop CS5 for Photographers - Martin Evening [62]
Virtual memory tricks
The Apple Macintosh and Windows operating systems are able to make efficient use of memory using their own virtual memory management systems. The Windows VM file should be set to at least 1.5 times your physical memory size.
Hard drive speed
Most desktop computers use internal drives which run at 7200 rpm and you can easily find spare internal drives that run at this speed or faster. For example, there are drives that even run at 10,000 or 15,000 rpm, but these are hard to come by and are expensive, plus they are more limited in disk capacity. Laptop computers usually have slower hard drives fitted as standard (typically 5400 rpm). It may therefore be worth checking if you can select a faster speed hard drive as a build-to-order option. External SATA drives (eSATA) are now regarded as faster than FireWire 800 and are sometimes available as multiport drives like the LaCie d2 series. In theory these are better.
RAID setups
RAID stands for Redundant Array of Independent Disks, and a simple way to explain RAID is that it allows you to treat multiple drives as a single drive volume to provide either increased data integrity, capacity, transfer rates or fault-tolerance compared to a single volume. How it does this depends on the RAID level you choose. You need a minimum of two disks to configure a RAID system and most off-the-shelf RAID solutions are sold as a bay dock that can accommodate two or more drives with a built-in RAID controller. A RAID disk can be connected via internal SCSI or using an external FireWire 400/800 connection.
RAID 0 (striping)
A RAID 0 setup is an ideal choice for use as a Photoshop scratch disk. With a RAID 0 setup, two or more drives are striped together to create a single large volume drive. For example, if two 400 GB drives are striped using a RAID 0 setup you will end up with a single 800 MB volume. RAID 0 is useful where you require fast hard drive access speeds, because the drive access speed increases proportionally to the number of drives that are added. So, if you have a 2 × 400 GB drive RAID 0 system, the hard drive access speed should be two times that of a single 800 GB drive. A RAID 0 setup can offer faster speeds but will be less reliable, since if one drive fails, all the stored data is lost on the combined volume.
Software RAIDs
It used to be the case that software-created RAIDs such as the one included with the Mac OS X Disk Utilities program were a lot slower than a dedicated system. True, the read/write speeds from a software RAID will still be somewhat slower than a true dedicated RAID system since a software RAID will be stealing some of your computer processor cycles, but these days the speed loss is not so bad as it used to be. For example, a software-driven internal striped RAID 0 can bring about a 45% increase in disk access speed. Overall I recommend that if you do choose to go down the internal RAID route, you use a dedicated device with a RAID controller.
RAID 1 (mirroring)
A RAID 1 setup stores duplicate data across two drives. This means that if you have, say, two 400 GB drives configured in a RAID 1 setup, the data on one drive is mirrored on the other and the total drive capacity will be equal to that of a single drive (in this case, 400 GB). RAID 1 systems are used as a way to protect against sudden drive failure since if one drive fails, a mirror copy of that data can immediately be accessed from the other drive and if you replace the defunct drive with a new one, the RAID 1 system rebuilds a copy