The main difference between the drives (ST20000NM007D, ST20000NM002D, ST18000NM003D, ST18000NM000D, ST20000NM000D, ST20000NM003D, ST18000NM004D, ST18000NM001D, ST20000NM005D, ST18000NM002D) is the model number, and each of them corresponds to a different hard drive model, with different features and technical specifications.
The first three characters of each model number (ST2, ST1 and ST1) indicate that these are Seagate hard drives. The following four digits indicate the capacity of the drive, for example, ST20000NM007D is a 20TB drive, ST18000NM003D is a 18TB drive.
The next two characters indicate the type of the drive, NM stands for Nearline SAS, which is a SAS hard drive for enterprise storage systems.
The last three digits of the model number are unique to the specific drive model, which could indicate different features, performance, or other aspects of the drive.
According to Seagate's product specifications, the Seagate Exos X20 ST18000NM003D 18TB hard drive has an operating noise level of 6.8 bels and an idle noise level of 4.6 bels. These values are the average noise level measured at a distance of 1 meter from the front of the drive.
To convert bels to decibels (dB), you multiply the number of bels by 10. So 6.8 bels is equal to 68 dB and 4.6 bels is equal to 46 dB.
It's worth noting that these are the manufacturer's specifications and the actual noise level of a hard drive may be different depending on the specific environment and setup in which it is used. In general, a noise level of 68 dB is considered to be quite loud and could be heard in a quiet room, similar to the noise level of a vacuum cleaner. A noise level of 46 dB is relatively low and it is unlikely to be heard in a typical office environment.
ST20000NM007D, ST20000NM002D, ST18000NM003D, ST18000NM000D, ST20000NM000D, ST20000NM003D, ST18000NM004D, ST18000NM001D, ST20000NM005D, ST18000NM002D.