Disaster Recovery tiers have been defined in the early 1990s by the Automatic Remote Site Recovery project at SHARE and are as follows:
| Tier 0 | No Disaster Recovery plan. All data is lost and recovery is not possible. |
| Tier 1 | Pickup Truck Access Method (PTAM) – the system, the subsystem, and the application infrastructure, along with application data, is dumped to tape and transported to a secure facility. All backup data, such as image copies and archived logs that are still onsite will be lost in the event of a disaster (typically up to 24-48 hours of data). Recovery from a disaster involves securing a DR site, installing IT equipment, transporting backup tapes from the secure facility to the DR site, restoring the system, the subsystem, and application infrastructure along with related data, and restarting the workload (typically taking a number of days). Cost factors include securing a site to perform the recovery, creating the backup copy of data, backup tape transportation, and backup tape storage. |
| Tier 2 | PTAM and Hot Site – same as Tier 1 except the enterprise has secured a DR facility in advance. Data loss will be up to 24-48 hours, and recovery will take 24-48 hours. Cost factors include owning a second IT facility or a DR facility subscription fee, in addition to the Tier 1 cost factors. |
| Tier 3 | Electronic vaulting – same as Tier 2 except that the enterprise dumps the backup data to a remotely-attached tape library subsystem. Data loss will be up to 24 hours or less (depending upon when the last backup was created) and the recovery duration will typically be 24 hours or less. Cost factors include telecommunication lines to transmit the backup data and a dedicated tape library subsystem at the remote site, in addition to the Tier 2 cost factors. |
| Tier 4 | Active Secondary Site (electronic remote journaling) – same as Tier 3 except that transaction managers (TM) and Data Base Management System (DBMS) updates are remotely journaled to the DR site. The amount of data loss will be minutes to hours, and the recovery time will be 24 hours or less (the recovery time could be reduced to 2 hours or less if updates are continuously applied to a shadow secondary DBMS image). Cost factors include a staffed, running system in the DR site to receive the updates and disk to store the updates, in addition to the Tier 3 cost factors. |
| Tier 5 | Two-Site Two-Phase Commit – same as Tier 4, with applications performing two-phase commit processing between two sites. Data loss will be seconds and the recovery time will be 2 hours or less. Cost factors include modifying and maintaining the application to add the two-phase commit logic, in addition to the Tier 4 cost factors. |
| Tier 6 | Zero Data Loss (remote copy) – the system, the subsystem, and application infrastructure along with application data is mirrored (copied) from the production site to a DR site. There will be small to zero data loss if using synchronous remote copy, and seconds to minutes if using asynchronous remote copy. The recovery window will be the time required to restart the environment using the secondary disks if they are data consistent (typically less than 2 hours); however, experience has shown that DBMS data at the remote site is unusable in the case of a disaster when using any form of synchronous remote copy. Cost factors include the cost of the telecommunications lines to shadow all of the data updates in real time, in addition to the Tier 4 cost factors. |
| Tier 7 | Geographically Dispersed Parallel Sysplex (GDPS) – GDPS is beyond the SHARE-defined DR tiers because it provides total IT business recovery through the management of processors, systems, and storage resources across multiple sites. GDPS manages not just the physical resources, but also the application environment and the consistency of the data, providing full data integrity (across volumes, subsystems, operating system platforms, and sites), while providing the ability to perform a normal restart in the event of a site switch, thus keeping to a minimum the duration of the recovery window. |
If you’ve been promoted to manager and you’re new to business administration, disaster recovery is probably the first tasks you must start knowing. This is particularly important (and vital) if you’re in a place where natural disasters like storms and floods occur regularly.’..
The most common “data recovery” scenario involves an operating system (OS) failure (typically on a single-disk, single-partition, single-OS system), in which case the goal is simply to copy all wanted files to another disk. This can be easily accomplished using a Live CD, many of which provide a means to mount the system drive and backup disks or removable media, and to move the files from the system disk to the backup media with a file manager or optical disc authoring software. Such cases can often be mitigated by disk partitioning and consistently storing valuable data files (or copies of them) on a different partition from the replaceable OS system files.^:
Until next time