AHCI vs RAID
AHCI (Advanced Host Controller Interface) is a mode of operation that was defined by Intel for the SATA interface. It does not affect the speed of the SATA interface in any way but allows the usage of more advanced features inherent in SATA. On the other hand, RAID (Redundant Array of Inexpensive Disks) is a much older technology that predates even the SATA technology. It is a method of improving the performance or the reliability by using additional hard drives. Since AHCI was created by Intel, this functionality is used by their chipsets only and computers that do not use the Intel chipset are unable to use AHCI, unlike RAID which has been pretty standardized and can be obtained and used by a wide variety of manufacturers.
RAID is a very old technology and is much older to AHCI and even SATA. There are configuration definitions that indicate how the RAID array is meant to work. RAID 0 improves the read/write speeds by striping the data into several drives so that it only takes a fraction of the time to write or read data. RAID 1 duplicates the content of one drive to another so that in case one fails, data is still retained in the other drive. There are several more configurations defined that either improves performance, reliability or both.
RAID has also become an operating mode in SATA along with AHCI and IDE. In terms of features, it basically exposes the same feature set that is available in AHCI making them identical in single disk applications. RAID truly shines when you go into multi disk configurations where you can utilize its more advanced features because AHCI is unable to operate in this mode. But using RAID can become very expensive once you start adding more disks into your array.
Summary:
1.AHCI is more of an operation for SATA drives while RAID is an advanced mechanism that provides performance enhancements by using multiple hard drives in different configurations.
2.RAID is a much older technology compared to AHCI.
3.AHCI is pretty much exclusive to computers with Intel chipsets while RAID functionality is offered by a wide variety of vendors.
4.RAID mode in SATA also exposes the same functionality that AHCI does.
5.RAID is more advantageous for people compared to AHCI if they are willing to spend extra cash on additional hard drives.