Managing RAID on Linux

The Linux Virtual Filesystem (VFS)

The Virtual Filesystem (VFS) was developed to provide a common interface for many filesystems to interoperate with the Linux kernel. The VFS is an additional layer of abstraction between specific filesystem implementations and system calls. Figure 6-1 illustrates the relationship between filesystems, block devices, and the VFS.

Figure 6-1. The Linux Virtual Filesystem.

The Linux kernel and the VFS impose some limits that affect the usability of any filesystem. Originally, the Linux file access API used a signed 32-bit value to represent file sizes on 32-bit systems such as x86 and PowerPC. This imposed a serious limit because file size could never be larger than a single 32-bit value. Using 32-bit values to store file sizes limits users to a maximal file size of 2³¹ (2,147,483,648) bits or 2 GB. Beginning with the 2.4 series kernel, this limit was raised to 1 terabyte (TB) or 1000 GB. Patches to correct the 2 GB limitation are available for 2.0 and 2.2 series kernels. Libraries and applications must also be patched if you want large file support. So even with a patched kernel, not all applications will support large file sizes natively. For more information on large file support, see http://www.suse.de/~aj/linux_lfs.html. Also note that many distributions that shipped 2.0 and 2.2 series kernels came with large file support already implemented. Check ...