File Systems and Volume Managers: History and Usage Page 2


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Standard Volume Manager (VM) Inner Workings (Striping)

Most file systems require a VM to group disk and/or RAID devices together, typically via striping. Striping spreads the data across the devices based on the stripe size set within the volume manager. The idea behind striping is to spread the data across multiple devices to improve performance and to allow multiple I/O disk heads to be seeking simultaneously. It should be noted that some volume managers support something called concatenation, which starts with an initial device and then begins writing to a second device only after the first has become full.

The following examples show what happens under standard striping when writing multiple files at the same time (first illustration) and what happens when one of those files is removed (second illustration).

File Systems that Maintain Their Topology

Some modern file systems maintain and understand the device topology without a volume manager. These file systems support both striping and something called round-robin allocation. Round-robin allocation means that each device is used individually. In most cases, each file open moves to the next device. In some file systems, it could be that each directory created moves to the next device. Here is an illustration of round-robin allocation:

As we will see, round-robin allocation has some other important implications for performance as well.

Page 3: File Allocation Comparison

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