First some background: I use my workplace office to store my file backups. To keep them private They are in multiple large files encrypted with TrueCrypt. The encrypted files range from 24 GB to 150 GB. I copy them to disk and take the disk to work.
I was testing file transfer speeds for these large file transfers.
My boot drive is a 120 GB RevoDrive (PCIe RAID SSD, marketed as read 540 MB/s, write 490 MB/s). I am running Windows 7 64 bit with an AMD Phenom II X6 1090T at the standard 3.2 GHz. The RevoDrive started with 25 GB occupied.
All files transfers mentioned below were by drop and drop in Windows Explorer using the same 24 GB file. The transfer started fast then slowed down so I took the transfer rate when half the file transferred (12 GB). The transfer rates were those shown by Windows Explorer.
To start I copied the file to the RevoDrive since it is my fastest drive. The file was on a Seagate 500 GB Barracuda 7200.11 HDD. It copied to the RevoDrive at a rate of 67 MB/s.
I copied from the RevoDrive to an AData 64 GB SSD (marketed as read 280 MB/s, write 270 MB/s) connected by eSata. I got the same transfer speed, 67 MB/s! The AData started with only 27 GB free space so the transfer came close to filling it.
I copied from the RevoDrive to an empty Seagate 320 GB Barracuda 7200.11 HDD. The transfer speed was 96 MB/s.
I copied from the RevoDrive to an Maxtor 500 GB DiamondMax-11 HDD. It had 200 GB occupied. The transfer speed was 27 MB/s.
I deleted the file from the AData SSD and connected it with a USB 3.0 adapter. The transfer speed from the RevoDrive to the AData was 97 MB/s.
I copied from the RevoDrive to an empty GSkill Falcon 128 GB SSD (marketed as read 230 MB/s, write 190 MB/s) connected by eSata. The transfer speed was 116 MB/s.
I copied the file from the AData SSD (USB 3.0) to the GSkill SSD (eSATA), which now had 24 GB occupied. The transfer speed was 64 MB/s. This was the only transfer that started slow (47 MB/s) and increased in speed as the file was copied.
I deleted the file from the AData and copied it back from the GSkill to the AData. The transfer speed was 66 MB/s.
I tried all of these tests to compare file transfers within the computer. Before running these tests I transferred these files (24 GB, 45 GB, 120 GB, 150 GB) from a Seagate 500 GB HHD to another computer over gigabit ethernet using Windows file sharing. The other computer was running Windows 7 64 bit on an AMD Athlon 64 X2 6000+ at 3 GHz. It was booting off the the AData 64 GB SSD that I borrowed for the above tests. This computer had four 300 GB 10,000 rpm VelociRaptor HDDs connected in RAID 10 using the Asustek motherboard's RAID controller. The files transferred at 90-95 MB/s.
Sounds frustrating. What OS is the primary machine running, or did you put that and I missed it? Write speeds to SSDs can degrade, as you probably already know, if the TRIM command is not getting sent. But it sounds like you are reading from the SSD and copying to other devices. What kind of motherboard?
You did some pretty thorough copy testing! I would suggest also doing a quick bench of each individual drive that you are using, both read and write, to see if that identifies a bottleneck.