File Systems and Volume Managers: History and Usage - EnterpriseStorageForum.com

File Systems and Volume Managers: History and Usage

Over the last few months we have reviewed the data path from the application through the operating system. The next step in the data path is the file system, and the volume manager that accompanies most file systems.

The file systems as we know them today trace their roots to a proposal for the Multics operating system in 1965. (See http://www.multicians.org/fjcc4.html for more details.) This proposal for all intents and purposes became the Unix File System file (UFS) in the early 1970s and remains the UFS as we know it today. Not much has changed in file systems over the last 35 years -- they recover faster and support larger files and file systems, of course, but these are evolutionary changes rather than radical changes. Compare the changes in file systems to the hardware changes that have been made over the same period of time, and you'll see only incremental change overall at best.

In my opinion, the file system (and the associated volume manager) is the most critical component in the data path due to its ability to dramatically affect I/O performance. Even the best file system and volume manager available today can be improperly configured to the point that performance is horrible.

File System (FS) Basics

The purpose of file systems is to maintain a consistent view of storage so that we can effectively manage it. This is done in a way that allows the users to create files and directories as well as delete, open, close, read, write and/or extend the files on the device(s). File systems also maintain security over the files that they maintain and, in most cases, access control lists for a file.

Volume Manager (VM) Basics

Volume management was developed in the late 1980s to enable the creation and management of file systems larger than a single disk, which offered the possibility for greatly improved performance. Since almost all file systems at that time could only mkfs (create a file system) a single device, volume mangers provided file systems a single set address range for multiple devices. Other volume manager enhancements in the 1990s included support for software RAID 1 and 5.

Page 2: Standard Volume Manager (VM) Inner Workings (Striping)



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