internal drives with different speed rates Mac Pro (Mid 2012)

I have four drives in one of the Mac Pro (2012)

• 1 Disc Operating
• 2 Disc Dedicated to FCPX (Libraries
• 3 Disc Media Strorage (Documents etc)
• 4 Disc Backup

When I run a Speed test on all four drive here are my results.

• 1 Disc Write 112 MB/Sec - Read 110 MB/Sec
• 2 Disc Write 96 MB/Sec - 99 Read MB/Sec
• 3 Disc Write 72 MB/Sec - 72 Read MB/Sec
• 4 Disc Write 61 MB/Sec - Read 61 MB/Sec

Why the speed differences? Sense years it has been told not to use the OS (Prime) drive as scratch drive do to the lack of performance.
But here it clearly shows as the fastest drives.

All drives are the same model.

Using a different drive for Libraries and media is not about the speed of the drive, it is about the limited bandwidth the CPU can read/write to the drive. Video eats up that bandwidth a lot, and the OS and apps need bandwidth to function quickly and properly.

Just like your Internet connection, you can only upload and download so much data per second. Your hard drives have the same type of connection. There is a limit to how much data can be send up and down that wire per second.

Are all drives the same capacity?

Also, drive speed tests should be done at least 4 times, if not 6 or 10, and then averaged out for an "average" read/write speed. There is no absolute read/write speed for a drive. What manufacturers list on the boxes is a maximum possible read/write speed, which you'll never see in real world use.

Several things can effect the read/write speeds of drives. Bandwidth of hardware connections between HDD and CPU. How much data is on the drive. Block and sector size the drive was formatted with. OS accessing it. Format of the drive. Health of the Directory on the drive. Efficiency of a specific app's coding which is manipulating the data on the drive. Frequency of data being accessed by a specific app (more frequency means more RAM read/writes, which then get buffered to/from the drive's read/write process).

Your drives seem to all be in the same neighborhood, so I'd consider them pretty equal, and I think I could guess which ones have more or less free space on them. List the percentage of free space on each, see if there is a correlation.

Yes all drives are identical

• 1 Disc 1 TB used 530 GB
• 2 Disc 1 TB used 200 GB
• 3 Disc 1 TB used 370 GB
• 4 Disc 1 TB used 736 GB

All drive have been repaired and verified with Disk Utilities with no errors.
As you advised I ran the AJA Disk Test for 10 min on all drives with the following results.

• 1 Disc Write 107 MB/Sec - Read 108 MB/Sec
• 2 Disc Write 98 MB/Sec - 97 Read MB/Sec
• 3 Disc Write 74 MB/Sec - 73 Read MB/Sec
• 4 Disc Write 62 MB/Sec - Read 63 MB/Sec

I didn't advise running for 10 minutes. I advised doing 10 individual tests, and averaging the results.

I'd also advise running Disk Warrior to repair the directories on each, to more level the playing field.

But yes, multiple of the same make/model drive can give different results. That is not unusual.