Parallel I/O

Windows NT Server also has built-in disk partitioning. It allows logical volumes to be spread across multiple physical volumes. Each logical volume can be a RAID or it can be an individual disk. Windows NT Server has the following software support:

RAID 0—striping a logical volume across multiple physical volumes.
RAID 1—disk mirroring or shadowing in which data is replicated on multiple disks.
RAID 5—a fault-tolerant storage strategy in which disks are organized so that one stores parity for data on the others. RAID 5 is more space-efficient than RAID 1.

This software support lets Windows NT Server customers build reliable storage with commodity controllers and disks. RAID also offers partition parallelism since it spreads the data among multiple disks that can be read in parallel.

Windows NT Server can read individual commodity SCSI disks at their rated speed of 8 MB/sec and can drive SCSI controllers at speeds of 18 MB/sec. By using a PCI-based (peripheral component interconnect) machine and by striping data across 4 SCSI controllers, a single commodity Pentium processor running Windows NT Server has been clocked reading a disk array at 60 MB/sec. This means that a single Pentium processor can read or write data at 200 GB per hour. These rates are important for data-intensive operations like data loading, backup, data indexing, and data mining.

These are impressive numbers for any computer, but they are especially impressive when using commodity single-processor systems. By using multiple processors and multiple PCI buses, SMP systems can read and write data at even higher speeds and still have power left over to analyze and process the data.