Disk-Array

A disk array ( Germanized disk subsystem or disk subsystem ) is a device with multiple hard drives, the servers will be provided. Functions such as RAID, storage virtualization, copies or reflections within the same or between disk arrays are performed directly on these without the participation of the server.

History

The first disk arrays were simple external hard drive enclosure without RAID functionality (JBOD ). Modern disk arrays have multiple independent controllers to high availability through redundancy, high data transfer performance by load balancing and parallel access from multiple servers simultaneously (often via a Storage Area Network) to enable. Also common is the use of cache subsystems. This writing is already reported to the operating system back to be complete when the data has been stored in the cache of disk arrays, but were not physically stored on the hard drives. This will affect the write performance of the overall positive.

Initially it was connected via SCSI. In the late 1990s Fibre Channel prevailed as usual interface. Depending on the application is also iSCSI attachment conceivable. In the mainframe environment ESCON and FICON are common protocols.

Trivia

Frequently single disks can be used or replaced during operation ( Hot-plug ). To this end, each disk requires a special mounting frame. Hot spare disks can be configured to accept data from a failed hard drive in case of failure.

Modern disk arrays can manage hundreds of hard drives and capacities of up to several hundred terabytes and have caches of several gigabytes. As examples, the EMC Symmetrix DMX-3 were useable with 525 TB capacity to 2400 disks with 256 GB cache and usable HP XP 12000 with 332 TB capacity 1152 hard drives with 128 GB of cache (both in the theoretical maximum configuration ) called. (As of end of 2006).

The name "sub- system " derives from the interplay between the respective plate system and the actual main computer on which to run the applications from.

Examples

EMC CLARiiON CX500 with the cover removed on a disk shelf

EMC Symmetrix DMX1000. In the upper part there are the hard drives in the lower controllers, power supplies and UPS. Right of control laptop.

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