Microsoft SQL databases have two components: Transaction Logs (.LDF) and Databases (.MDF).    Transaction Logs are designed to keep track of each transaction with the database.   If properly configured, they can provide some fault tolerance to failures.

Active Directory Domain Services uses AdminSDHolder, protected groups and Security Descriptor propagator (SD propagator or SDPROP for short) to secure privileged users and groups from unintentional modification. This functionality was introduced in the inaugural release of Active Directory in Windows 2000 Server and it’s fairly well known.

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Many technology hardware and software vendors take a very hard-line on support contracts.  No support or maintenance contracts means no support.  Some vendors will sell you “per incident” support.  Some won’t.  With software vendors you also get into the issue of software upgrades being tied to software maintenance.

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A well designed rack environment would include cold aisles (in front of the equipment with the AC vents) and hot aisles (behind the equipment with the air returns). Then the racks would have no gaps between the rack mounted equipment. If there are gaps between the equipment, then spacers are added to block air flow.