RAID 0: Disk Striping for greater performance.
RAID 1: Disk Mirroring for greater reliability
and performance.
RAID 2, 3, 4 and 5: Disk Striping with Parity
for reliability with minimal overhead.
RAID systems can be implemented in hardware or in software.
Hardware RAID systems are, basically, fancy disk controllers. Sometimes they come as a card you plug into your computer bus, sometimes they come in a box or rack along with their disks. These systems can be high cost, but the separate hardware is often tuned to the disks, and produces better results if it is still modern. It is also easier to manage, as the RAID and the operating system don't interfere with each other much.
Software RAID systems are, basically, fancy disk drivers that fit under your file system. You supply the disks, which are usually SCSI or FireWire. These systems are often built into your operating system, and so all you pay for is disks and maybe a nice controller or set of controllers. For instance, SUSE Linux comes with RAID software that combines partitions you specify into a device named /dev/md0, /dev/md1, etc. Software RAID can complicate matters, though, because they are trickier to get right. You get what you pay for.
All RAID systems are tricky to get right. It has been said that each RAID implementation is a different story for a different reason, and so it helps a lot to know what you are doing, and why you are doing it. The "reliability" is a protection against a mechanical disk failure, for instance, and won't protect against accidental erasure. The speed increases typically won't happen if you use two partitions of the same disk, and might not happen if you use the one controller for all the disks. Unless you are using cutting-edge disks, you are likely to get better performance by simply buying a big, modern, fast disk. In all cases, you must monitor performance and fine-tune the details for your particular situation.
See also Execute Permission and Write Permission.
Volumes have a restriction on the size of a regular file; in particular all files must fit within the volume, and specifically no file can deplete more than the total for the volume.
- The root of the filesystem is the directory "/". Most users have permission to read that directory, but usually only the superuser has permission to add or remove files.
- The root directory of a volume is the highest directory. All other files on the volume are ultimately contained in the root directory of the volume. When a volume is mounted on a mount point, the mount point's previous contents are hidden by the root directory of the new volume.
- The root volume on a computer is the volume mounted at the root, at "/".
- The user named root is the superuser. Often, their home directory is "/", which is where the username came from, but on some systems there is a special directory for this purpose such as /root.
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