The OS/2 Raw File System provides an interface for applications to efficiently manage data on the logical partitions or physical hard drives installed in a system. Some of the Raw File System function is available by using a combination of the DosPhysicalDisk and DosDevIOCtl functions. However, the Raw File System provides a significant step forward in usability and performance.
The Raw File System provides a programming abstraction that treats each logical partition or physical disk as one large file that can be opened, locked, seeked, read from, written to, and closed.
Logical partitions are identified using the Universal Naming Convention (UNC) in the form of
\\.\X:
where X can be substituted with the letter corresponding the logical partition desired on any hard drive, floppy disk or CD-ROM drive.
Physical disks are identified using a UNC name in the form of
\\.\Physical_Disk#
where # is replaced with the physical disk number corresponding to the number found in the FDISK utility. The Raw File System recognizes up to 128 physical disks, thus eliminating the limit of 26 drives in previous versions of OS/2.
The use of the universal naming convention coupled with the ability to access any physical or logical drive using the common file system functions in OS/2, provides a greatly simplified migration path for applications.
Traditionally, raw file systems have been utilized by applications that manage large amounts of data under heavy workloads. Typically, this has been commercial database servers performing on-line transaction processing. Disk I/O can become a bottleneck under these conditions and the use of an efficient raw file system can be very useful in improving system performance, through reduced path length and serialization. The chapter describes the Raw File System functions in detail.