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DRBD® software is a distributed replicated storage system for the Linux platform. It is implemented as several userspace management applications and some shell scripts and is normally used on high availability (HA) computer clusters. DRBD also refers to the logical block devices provided by the scheme and to the software that implements it. ''DRBD device'' and ''DRBD block device'' are also often used for the former. The DRBD software is free software released under the terms of the GNU General Public License version 2. DRBD is part of the Lisog open source stack initiative. ==Mode of operation== DRBD layers logical block devices (conventionally named /dev/drbd''X'', where ''X'' is the device minor number) over existing local block devices on participating cluster nodes. Writes to the ''primary'' node are transferred to the lower-level block device and simultaneously propagated to the ''secondary'' node. The secondary node then transfers data to its corresponding lower-level block device. All read I/O is performed locally. Should the primary node fail, a cluster management process promotes the secondary node to a primary state. This transition may require a subsequent verification of the integrity of the file system stacked on top of DRBD, by way of a filesystem check or a journal replay. When the failed ex-primary node returns, the system may (or may not) raise it to primary level again, after device data resynchronization. DRBD's synchronization algorithm is efficient in the sense that only those blocks that were changed during the outage must be resynchronized, rather than the device in its entirety. DRBD is often deployed together with the Heartbeat cluster manager, although it does integrate with other cluster management frameworks. It integrates with virtualization solutions such as Xen, and may be used both below and on top of the Linux LVM stack. DRBD version 8, released in January 2007, introduced support for load-balancing configurations, allowing both nodes to access a particular DRBD in read/write mode with shared storage semantics. Such a configuration requires the use of a distributed lock manager. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Distributed Replicated Block Device」の詳細全文を読む スポンサード リンク
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