Volume Management and File Systems Usage and Implementation

  Henry Newman

Current file systems trace their roots from the UFS file system, which was proposed in 1965. By the early 1970s, the UNIX file system was up and running. Since then, not much has changed in file systems and there have only been incremental hardware changes. I think the file system and volume manager are the most critical components in achieving I/O performance from both the OS and underlying hardware. Even the best file system and volume manager can be configured so that the performance is poor. Therefore, my next couple of columns will cover file system and volume management, in addition to file system configuration and tuning.

File System Basics

The purpose of file systems (FS) is to maintain a view of the storage so we can create files. This is done so that users can create, delete, open, close, read, write, and extent files on the device(s). File systems can also be used to maintain security over files.

Volume Manager Basics

The original goal of the UNIX volume management (VM), which was developed in the late 1980s, was to group disk devices together so that file systems larger than a single device could be created, and to achieve high performance by striping devices. Since file systems could only mkfs a single device, volume managers provided that single device, and features were added to support software RAID.

Standard VM Inner Workings (Striping)

Most file systems require a VM to group disk and/or RAID devices together. Striping spreads the data across the devices based on the stripe size set within the volume manager. Note that some volume managers support concatenation, which starts with the first device and then only writes to the next device when the first device becomes full.