Thank you for purchasing through links and ads on this site.
diglloyd Deal Finder...
Buy other stuff at
Upgrade the memory of your 2018 Mac mini up to 64GB
Handpicked deals...
$2399 $2159
SAVE $240

$200 $160
SAVE $40

$1499 $1148
SAVE $351

$590 $472
SAVE $118

$1299 $997
SAVE $302

$1199 $1015
SAVE $184

$1480 $1230
SAVE $250

$3999 $2499
SAVE $1500

$1498 $1098
SAVE $400

$2897 $1797
SAVE $1100

$399 $399

$899 $699
SAVE $200

$3297 $1897
SAVE $1400

$749 $499
SAVE $250

$799 $567
SAVE $232

$870 $749
SAVE $121

$3499 $2199
SAVE $1300

$3599 $2299
SAVE $1300

$4499 $2650
SAVE $1849

$750 $600
SAVE $150

$899 $699
SAVE $200

$799 $729
SAVE $70

$3599 $2299
SAVE $1300

$3499 $2199
SAVE $1300

$4499 $2650
SAVE $1849

$1997 $897
SAVE $1100

$3099 $2499
SAVE $600

$2799 $2199
SAVE $600

$4999 $4599
SAVE $400

$4499 $2650
SAVE $1849

Save Big $$$$ on Memory for 2019 Mac Pro

Up to 65% better pricing than Apple

Lloyd recommends 32GB RDIMM modules for most users (more expensive LRDIMMS are for 512GB or more).

Photoshop CS4 oddities

Last updated 2009-06-01 - Send Feedback
Related: optimization, Photoshop, RAID, software

This page contains Photoshop observations made during the course of testing. See also Configuring Photoshop, Speeding up Saving/Opening, Monitoring System Performance and Storage.

Photoshop RAID performance perhaps not exploited

This is a programmer/nerd discussion, feel free to skip it.

Using 'iostat', it can be seen that only about 1/3 of the disk speed is exploited (based on extensive testing of my RAID setup). This appears to be an internal Photoshop bottleneck, since neither the disk bandwidth nor CPU cores are exploited more than fractionally: computation is neither CPU-bound nor I/O-bound; the I/O is underutilized as are the CPU cores. The operations in question are not ones resistant to parallel techniques.

This oddity led me to investigate—

Using Apple’s Instruments program for software developers, I recorded the numerous disk I/Os that Photoshop performs to its scratch disk. The test volume used a 32K RAID stripe size.

Photoshop PBReadSync size:  1051232 = 1MB + 2656 bytes
Photoshop PBWriteSync size: 1051648 = 1MB + 3072 bytes

The concern here is that the writes are done with a non-integral number of bytes relative to the stripe size: there are 3072 bytes “left over” that a single drive must handle, unless the OS can zero-pad the block those bytes fall into. It is unclear, based on varying usage scenarios and Mac OS X caching, whether this issue is responsible for failure to exploit available disk bandwidth with 3/4/5/6 drive striped scratch volumes. Reads are not at issue since whole blocks are always read.

DiskTester results (which bypass system caching) show that write speed drops from a median speed of 492MB/sec to 118MB/sec on a 6-drive striped RAID when 1025K chunks vs 1024K chunks are written on the 2nd and subsequent passes. A 2-drive stripe sees a 57% performance loss. Whether there are 2 or 3 or 5 or 10 drives in the stripe, write performance is limited to (roughly) the speed of a single drive. Whether the scratch drive is used in this manner in general Photoshop operation is unclear, but if so, it would be a major performance hit.

Adequate memory for caching seems to mask the performance loss. See the test results.

Adobe could eliminate this as a potential issue by always writing scratch data in integral multiples of the stripe size (this could be a preference setting to choose the size). Or choosing 128K would solve the issue for virtually all striped RAID configurations.


New Mac Pro?

Or iMac 5K or iMac Pro?
Consult with Lloyd ASAP before buying!

System configuration for CPU, GPU, memory, SSD, backup, RAID, optimizing performance, workflow.
For YOUR optimal workflow

Avoid costly mistakes in throwing money at the problem for less performance and/or buying the wrong machine for your own needs!

Remote screen sharing available for RAID, software configuration, etc.

More about 2019 Mac Pro vs iMac 5K vs iMac Pro...

View all handpicked deals...

SanDisk 512GB Extreme PRO UHS-I SDXC Memory Card
$200 $160
SAVE $40 | Terms of Use | PRIVACY POLICY
Contact | About Lloyd Chambers | Consulting | Photo Tours
Mailing Lists | RSS Feeds | Twitter
Copyright © 2019 diglloyd Inc, all rights reserved.
Display info: __RETINA_INFO_STATUS__