With onset of cheap, efficient, and very large hard drives, even simple home systems may employ several hard drives. The use of multiple hard drives opens up opportunities for ensuring storage reliability as well as more easily organizing access to your hard disks. Linux provides two methods for better managing your hard disks: Logical Volume Management (LVM) and Redundant Arrays of Independent Disks (RAID). LVM is a method for organizing all your hard disks into logical volumes, letting you pool the storage capabilities of several hard disks into a single logical volume. Your system then sees one large storage device, and you do not have to micromanage each underlying hard disk and its partitions. LVM is perhaps the most effective way to add hard drives to your system, creating a large, accessible pool of storage. RAID is a way of storing the same data in different places on multiple hard disks. These multiple hard drives are treated as a single hard drive. They include recovery information that allows you to restore your files should one of the drives fail. The two can be mixed, implementing LVM volumes on RAID arrays. LVM provides flexibility, and RAID can provide data protection.
With LVM you no longer have to keep track of separate disks and their partitions, trying to remember where files are stored on what partitions located in what drive. Partitions and their drives are combined into logical file systems that you can attach to your system directory tree. You can have several logical file systems, each with its own drive and/or partitions.
In a system with several hard drives, with both LVM and RAID, you could combine the hard drives into one logical file system, which accesses the storage as one large pool. Files are stored in a single directory structure, not on directories on a particular partition. Instead of mounting file systems for each individual hard drive, there would be only one file system to mount for all the hard drives. LVM has the added advantage of letting you implement several logical file systems on different partitions across several hard drives.
RAID is best suited to desktops and servers that hold multiple hard drives and require data recovery. The most favored form of RAID, RAID 5, requires a minimum of three hard drives. RAID, with the exception of RAID 0, provides the best protection against hard drive failure and is considered a necessity for storage-intensive tasks like enterprise, database, and Internet server operations. It can also provide peace of mind for smaller operations, providing recovery from hard disk failure. Keep in mind that there are different forms of RAID, each with advantages and weaknesses. RAID 0 provides no recovery capabilities at all. After setting up a RAID array, you could then implement LVM volumes on the array.
In comparison to LVM, RAID can provide faster access for applications that work with very large files, like multimedia, database, or graphics applications. But for normal operations, LVM is just as efficient as RAID. LVM, though, requires running your Linux system and configuring it from your Linux operating system. RAID, which is now supported at the hardware level on most computers, is easier to set up, especially a simple RAID 0 operation that merely combines hard drives into one drive.
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