Hard Disk Interfaces
by Jimmy Martin
For a web server to read and write data to and from its hard disk drives, there must be some kind of connection between the drives and the processor. These connections are known as interfaces. There are three main types of hard disk interface used in web servers.
PATA - This is also known as IDE (Integrated Drive Electronics) or simply ATA (Advanced Technology Attachment). PATA stands for Parallel ATA. It is used in low-end servers as it has been superceded by SATA.
SATA - Serial ATA. This is a newer, faster way of connecting a hard drive. It is based on ATA technology and it is faster than PATA when reading from the drive's cache buffer. It makes no difference when accessing large files, or small files that were not in the cache. This is because both PATA and SATA can transfer data faster than the drive's sustained transfer rate. Although SATA drives do not have as good performance or reliability as SCSI drives, they are available with larger capacities. A modern low- to mid-range web server should have SATA drives.
SCSI - Small Computer Systems Interface. This is used on high-end web servers. SCSI drives are usually faster and more reliable than SATA, but are not available in such high capacities. The speed and reliability come at a cost. SCSI drives are very expensive, but it is worth it for high-end servers. There is a version of SCSI known as Fibre Channel, which is extremely fast and expensive and is usually used only on specialized data storage servers.
Which drive interface your web server should have depends on the price and performance you are looking for. A low-end server may have PATA drives, while a high-end server would not settle for less than SCSI. Alternatively, a high-end server may have a mixture. SCSI drives could be used for storing frequently-requested files, while SATA drives would be used for bulk storage due to their higher capacity and lower cost.
Next we will look at ways of using several drives together to improve speed and reliability when we discuss RAID arrays.