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The hot spare disk reduces the mean time to recovery (MTTR) for the RAID redundancy group, thus reducing the probability of a second disk failure and the resultant data loss that would occur in any singly redundant RAID (e.g., RAID-1, RAID-5, RAID-10). Typically, a hot spare is available to replace a number of different disks and systems ...
An example is a server chassis that has three power supplies; the system may be set to 2+1 redundancy so that the blades can enjoy the power of two PSUs and have one available to give redundancy if one fails. It is also common to mix live (hot) redundancy where UPSes are online, and cold standby redundancy where they are offline until needed.
In engineering and systems theory, redundancy is the intentional duplication of critical components or functions of a system with the goal of increasing reliability of the system, usually in the form of a backup or fail-safe, or to improve actual system performance, such as in the case of GNSS receivers, or multi-threaded computer processing.
Choosing the type of backup site to be used is decided by an organizations based on a cost vs. benefit analysis. Hot sites are traditionally more expensive than cold sites, since much of the equipment the company needs must be purchased and thus people are needed to maintain it, making the operational costs higher.
Configurations can also be defined with active, hot standby, and cold standby (or idle) subsystems, extending the traditional “active+standby” nomenclature to “active+standby+idle” (e.g. 5+1+1). Typically, “cold standby” or “idle” subsystems are active for lower priority work.
The term "failover", although probably in use by engineers much earlier, can be found in a 1962 declassified NASA report. [2] The term "switchover" can be found in the 1950s [3] when describing '"Hot" and "Cold" Standby Systems', with the current meaning of immediate switchover to a running system (hot) and delayed switchover to a system that needs starting (cold).
There’s nothing quite like a warm, steaming cup of hot chocolate on a cold winter day — even more so if you’ve topped it with marshmallows, whipped cream, chocolate shavings… or all of those!
Efficient Redundancy Redundancy Granularity Initial release year Memory requirements (GB) Alluxio (Virtual Distributed File System) Java Apache License 2.0 HDFS, FUSE, HTTP/REST, S3: hot standby No Replication [1] File [2] 2013 Ceph: C++ LGPL librados (C, C++, Python, Ruby), S3, Swift, FUSE: Yes Yes Pluggable erasure codes [3] Pool [4] 2010 1 ...