In computer science, shared storage is to be understood as a jointly used permanent storage device, which can be accessed jointly and possibly simultaneously (concurrently) by several computers via a network or other connection. The read-only memory typically consists of a so-called disk array .
Classic shared storage applications are active / passive clusters or failover clusters . All systems in this cluster access the same storage. In the event of a failover , a backup system can immediately replace the failed system, since both physically access the same database. Simultaneous access is impossible in an active / passive cluster, since exactly one system is always active while the others wait for a failover.
The situation is different with an active / active cluster : In this, two or more computers are active at the same time and may, under certain circumstances, have competitive access to the shared storage data. A typical example of an active / active cluster is the Oracle Real Application Cluster .
A local hard drive on a computer cannot simply be used to enable shared storage. Instead, for example:
- SCSI storage: Direct connection with SCSI cable when accessing up to two computers
- iSCSI (Internet SCSI): a technology that encapsulates SCSI in IP, i.e. enables SAN-like access via IP network
- AoE (ATA over Ethernet): Encapsulates ATA commands in Ethernet frames
- FC (Fiber Channel): high-speed network that is mainly used to connect mass storage devices
- SAN (Storage Area Network): SAN connection between two or more computers
- NAS (Network Attached Storage): Access to the storage via network connection
The Distributed Replicated Block Device is also suitable for using local hard disks and creating additional reliability .
Relation to DB systems
In connection with the topic of distributed and parallel DB systems, shared disk means the existence of a common external storage device. The DB processing takes place on loosely coupled or locally or spatially arranged computers, each with a DBMS . " Shared everything " and " shared nothing " are other forms of expression.
- ↑ Techopedia: shared storage. Retrieved October 11, 2018 .
- ↑ High-Availability Storage with HA-LVM. February 26, 2015, accessed October 11, 2018 .
- ↑ a b c IBM: Demystifying Fiber Channel, and iSCS. Retrieved October 11, 2018 .
- ↑ What is: DRBD (Distributed Replicated Block Device). Retrieved October 11, 2018 .
- ↑ Thomas Kudraß (Ed.): Pocket book databases . Fachbuchverlag Leipzig, Munich 2007, ISBN 978-3-446-40944-6 , page 394.