I/O speed

Hello, just testing my servers i would like to know, wich is the principal factor, brand? RPM? capacity? raid?

1.- RAID10 4x3TB:

CPU model :  Intel(R) Xeon(R) CPU           L5520  @ 2.27GHz
Number of cores : 8
CPU frequency :  1600.000 MHz
Total amount of ram : 32099 MB
Total amount of swap : 4095 MB
System uptime :   14 days, 9:37,
I/O speed : io= 29.6 MB/s

2.- RAID10 4x1TB (just purchased)

CPU model :  Intel(R) Xeon(R) CPU E3-1270 v3 @ 3.50GHz
Number of cores : 8
CPU frequency :  800.000 MHz
Total amount of ram : 32068 MB
Total amount of swap : 16095 MB
System uptime :   4:17,
I/O speed : io= 358 MB/s

3.- SSD 256GB:

CPU model :  Intel(R) Xeon(R) CPU E3-1270 v3 @ 3.50GHz
Number of cores : 8
CPU frequency :  800.000 MHz
Total amount of ram : 32045 MB
Total amount of swap : 16095 MB
System uptime :   31 days, 8:54,
I/O speed : io= 244 MB/s

all are dedicated servers.