Upgrading MacPro early 2008 (many questions-advice welcome)

I think the size of your existing drives is in fact one of your bottlenecks, so I would disagree slightly with your idea that you need speed more than space. Adobe apps love big chunks of free space for scratch disk use and caches. Your setup also seems overly complicated.

Large fast drives are pretty cheap these days. You can get a 6 TB Toshiba for $200 and put it into a good external enclosure. You should also be able to install a 4TB drive inside a 2008 Mac Pro, preferably WD Black or HGST. A good enclosure for a 4TB or larger external will cost in the neighborhood of $75, from OWC.

I wouldn't invest in a bunch of tiny drives, whether they are "enterprise" drives or not.

Inateck makes an inexpensive USB 3 card.

You said "own 2 Seagate Technology ST2000DM001 HDD Barracuda 2TB SATAII 6Gb-s 7200rpm Cache Bare Drive "

Just what drive is this? I asks since SATAII is only 3 GB/sec while SATAIII is 6 GB/sec.

The difference in performance between rotating drives on a 3G Vs 6G SATA bus is...

... none whatsoever, since these drives are not bottlenecked by the SATA Bus. (Even a SATA-I bus is not a bottleneck to rotating drives). These drives can source one burst off the platters at about 150 MBytes/sec, (well under SATA-I speeds of 375 MBtyes/sec) and then you have to wait for the next burst.

I loved Seagates for many years, going back to their SCSI drives and ATA drives. They've had some compatibility and reliability problems since then, and I have been using mostly HGST since moving to Macs with SATA, with some WD Black and recently Toshiba. I think the most significant failure rates recently were in a line of Seagate 3TB drives.

I've never set up a fusion drive, but for your purposes, larger is probably better. I've been using Adobe apps since one of them was an Aldus app. Photoshop and InDesign have always worked best for me when I had large chunks of free disk space. If you are working with large, complex Photoshop images, and are allowing yourself a healthy number of History states, you need elbow room. Suppose you are working with a 500MB image, and have 25 History states. While that image is actively being worked on, you could conceivably have up to 25 preserved states of that 500GB image.

If your images are typically much smaller, you don't have to worry about scratch disk space as much, but it will still matter.

El Cap's Disk Utility is a step in the wrong direction. Some dumb choices were made, such as a non-resizable window. Whoever made that decision must never have worked on a computer that had more than one active drive attached to it. Maybe two.

SATA I, SATA II, and SATA III rotating magnetic drives are all backward compatible. There is no measurable performance difference when used in the Internal bays, which have a SATA II 3GBits/sec capability, as opposed to used with a card that is SATA III 6Gbits/sec capable.

When used in a RAID, best performance is seen with very large reads OR very large writes from the SAME large file. Switching to a different file, or Reading while Writing to the same Drive eliminates the RAID performance Boost.

Striped RAID has no ability to survive a drive failure. A failure in a striped RAID wipes out all the data recorded on it.

Mirrored RAID extends the time you have to make the repair after a failure, but does NOT eliminate the need for backup. RAID is NOT Backup.

Users have been really quick to set up RAID arrays because they are thought to be really FAST. A RAID adds unnecessary complexity and is only fast when used for only one function ta a time.

Sometimes you get better performance by using separate drives: One for Source files, one for Destination (finished edits), another for Scratch, another for System. You can think of it as a RAID is good when it can stay focused on one file, and any distractions from other work will slow it down.

System is the biggest offender, because there is a pattern there of reading and writing random small files all over the place, and on a RAID made of Rotating Drives, there is almost no performance boost. Every time you have to move the drive head to a different file, you endure an additional 10 to 20 milliseconds of dead time, and the RAID speedup does not kick in until you Read the second and subsequent LARGE block of data from the same file.

If you can use multiple drives for different functions, you may not need a RAID at all.

You can generally get drives at pretty good prices from B&H in NYC.

http://www.bhphotovideo.com/c/product/835056-REG/Hitachi_0S03355_4TB_SATA3_3_5_I NTERNL.html

http://www.bhphotovideo.com/c/product/1182861-REG/toshiba_hdwe160xzsta_x300_6tb_ 3_5_desktop.html

I should add that I have three of the notorious Seagate 3TB external drives. Normally I would never consider acquiring such drives, because I prefer to use decent enclosures that are easy to open, and choose exactly what drive to install. I want to be able to remove a drive from its enclosure easily if I need to use it internally or to rule out a problem with the enclosure should the drive begin to be unreliable. However, I wound up with these three because two of them were free and one was very cheap. One has been in daily service, as one of a couple of backup drives, and it has been fine except for a problem with its base. The enclosures on the three drives have removable bases that contain power and data connectors. In one case, the base failed, but Seagate was quick to respond and send me a new base to try, which has worked well. In theory this is a nice idea, and I have three bases that can be swapped as needed between the three drives: one Thunderbolt, one FW/USB2, and one USB3. But in practice, it hasn't been all that useful, and prying open the cases to extract the drives would not be fun. So I stick with OWC enclosures and buy drives separately.

Thanks for sharing the Sputnik pic! And good luck with the upgrades.