You’ve just upgraded your (possibly new) computer to include more memory (RAM) and/or you’ve added hard disks, particularly external ones and possible RAIDed them for performance.
How do you know the memory works reliably? How do you know the disks are delivering the expected performance don’t have sporadic errors? Save yourself a lot of grief by testing before you go into “production”.
My experience has been that that the reliability of Apple’s memory is exceptionally high, so you can probably rest easy if all you’ve done is order Apple parts. But if you’ve installed 3rd-party RAM, particularly bargain-basement stuff, you should not assume that your experience will be trouble-free.
Memory testing: memory that might work fine at an ambient temperature of 80° F or below might suddenly turn flaky as things warm up. ECC memory might begin to report errors. Non-ECC memory will simply crash the machine when the bad area(s) are encountered, and even ECC memory will do so if more than one bit fails in a byte. To forestall such issues, diglloydTools offers a machine and memory stress test. Let that run for 24 hours before assuming a new configuration is reliable.
If you haven’t already seen it, read All About Mac Pro Memory for background, particularly the Memory Reliability section.
Hard disks — internal hard disks are generally more reliable than external ones; there is no extra cabling that can be damaged or pick up RF interference. But with multiple disks, RAID configurations, heat buildup, etc, both internal and external hard disks should be check for reliability and performance. I recently had ordered four Samsung 1TB hard disks. I could not obtain consistent RAID performance with the Samsungs, and I found that one of the four disks was a “dud”, always 10% slower than the other three. That’s a serious problem for a RAID; one sluggard disk will slow the whole RAID down and cause “hiccups” in performance.
The de-facto standard for testing RAID and hard disks on Mac OS is my very own DiskTester. Reliable and proven over years of use, DiskTester is THE tool to use for testing both performance and reliability. That’s why various Mac vendors use it to test their products, it’s why barefeats.com and amug.com use it, etc.