Oracle-type segments are not needed for most Microsoft SQL Server installations. Instead, SQL Server can distribute, or stripe, data better with hardware-based RAID or Windows NT software–based RAID. Windows NT software–based RAID or hardware-based RAID can set up stripe sets consisting of multiple disk drives that appear as one logical drive. If database files are created on this stripe set, the disk subsystem assumes responsibility for distributing I/O load across multiple disks. It is recommended that administrators spread out the data over multiple physical disks using RAID.
The recommended RAID configuration for SQL Server is RAID 1 (mirroring) or RAID 5 (stripe sets with an extra parity drive, for redundancy). RAID 10 (mirroring of striped sets with parity) is also recommended, but is much more expensive than the first two options. Stripe sets work very well to spread out the usually random I/O done on database files.
If RAID is not an option, filegroups are an attractive alternative and provide some of the same benefits available with RAID. Additionally, for very large databases that might span multiple physical RAID arrays, filegroups may be an attractive way to further distribute your I/O across multiple RAID arrays in a controlled fashion.
Transaction log files must be optimized for sequential I/O and must be secured against a single point of failure. Accordingly, RAID 1 (mirroring) is recommended for transaction logs. The size of this drive should be at least as large as the sum of the size of the online redo logs and the rollback segment tablespace(s). Create one or more log files that take up all the space defined on the logical drive. Unlike data stored in filegroups, transaction log entries are always written sequentially and are not proportionally filled.
For more information about RAID, see SQL Server Books Online, your Windows NT Server documentation, and the Microsoft Windows NT Resource Kit.