The terms ERT, RTO, RPO are used in IT\u2019s \u201cBusiness Continuity and Disaster Recovery policy\u201d, and basically they are time characteristics (measured in seconds, hours etc.) of a disaster recovery<\/b> of a data system.<\/p>\n
In the article RT (Recovery Time) and RP (Recovery Point) definitions are used for defining RTO, RPO, and ERT. This approach may lead to a new understanding of the terms and further discussions.<\/p>\n
<\/p>\n
Disaster Recovery in a Nutshell<\/strong><\/h1>\nA \u201cdisaster\u201d here means an event resulting in user’s data loss and\/or a period when data was unavailable.<\/p>\n
A process of a disaster recovery may be described step by step this way:<\/span><\/p>\n\n- data system is \u201con service\u201d, is ON,<\/li>\n
- disaster occurs and the system is now \u201cout of service\u201d, is OFF,<\/li>\n
- recovery is started by\u00a0user’s request or by an automated request,<\/li>\n
- recovery is finished,<\/li>\n
- the system is \u201con service\u201d again, is ON again.<\/li>\n<\/ol>\n
![\"ERT,](\"https:\/\/academy.sqlbak.com\/wp-content\/uploads\/2017\/12\/ERT-RTO-RPO...-Disaster-Recovery-in-a-Nutshell-648x365.jpg\")
<\/p>\n
Often the moment of the disaster<\/i> and start of the recovery<\/i> are considered to start at the same time, but it is not always true.<\/p>\n
Say, a user has accidentally deleted a database, but did not notice it, and only the next day the user discovered the loss and sent to the data center a request for a recovery. In this example, there is a big gap between the moment of the disaster and start of the recovery, so these moments are not the same.<\/p>\n
We consider \u201cRequest for Recovery\u201d and “Start of Recovery” as the same moment because the request here must start the recovery immediately, even if in reality it does not happen.<\/p>\n
Recovery Time and Recovery Point<\/strong><\/h1>\nIn ERT<\/b>, RT<\/b>O, RP<\/b>O abbreviations<\/p>\n\n- RT<\/b> stands for \u2018Recovery Time\u2019, and it is a time interval,<\/li>\n
- RP <\/b>stands for \u2018Recovery Point\u2019, and it means a moment in time.<\/li>\n<\/ul>\n
The RT and RP terms can be used and discussed separately from ERT, RTO, RPO.<\/p>\n
![\"ERT,](\"https:\/\/academy.sqlbak.com\/wp-content\/uploads\/2017\/12\/ERT-RTO-RPO...-RT-and-RP.jpg\")
<\/p>\n
\n- Recovery Time<\/i> is a duration of the recovery process,<\/li>\n
- Recovery Point<\/i> is a point-in-time from which the data system restores the data after the disaster.<\/li>\n<\/ul>\n
Recovery Time<\/h2>\n
RT <\/b>(Recovery Time) is a period of time required for a data center to resume its former condition after a request for recovery.<\/p>\n
Recovery time can be expressed by the formula:<\/p>\n
RT = <time of resuming functioning> – <time of request for recovery><\/p>\n
RT is overall \u2018out of service\u2019 time interval, it can include the time for trying to fix the problem without specific recovery efforts, the recovery itself, testing, and the communication to the users.<\/p>\n
Recovery Point<\/h2>\n
RP <\/b>(Recovery Point) is a point in time from which the data center restores the data after the disaster.<\/p>\n
The RP point in time may be defined in different ways, it can be<\/p>\n
\n- some \u201castronomical\u201d time, e.g., 01-JAN-2018 10:11:33<\/i>,<\/li>\n
- measured starting from the moment of the disaster, e.g., \u201c6 seconds before the disaster<\/i>\u201d.<\/li>\n<\/ul>\n
\u201cAstronomical\u201d time RP is used when considering data unavailability.<\/strong><\/p>\nThe duration of data unavailability time interval can be expressed here by the formula:
\n<data unavailability time> = <time of resuming functioning> – RP<\/p>\n
\u201cBefore the disaster\u201d approach of defining RP is used when considering a data loss.<\/strong><\/p>\nThe duration of lost data time interval can be expressed here by the formula:
\n<lost data time> = RP<\/p>\n
ERT, RTO & RPO\u00a0Definitions<\/h1>\n
Usually ERT, RTO, RPO are defined without using definitions of RT and RP, but they can be used.<\/p>\n
ERT – Estimated Recovery Time<\/strong>\u00a0<\/span><\/h2>\nERT is the estimated Recovery Time.<\/strong><\/em><\/p>\nThe common definition<\/a> without using RT definition:<\/p>\nThe estimated duration for the database to be fully functional after a restore\/failover request<\/em>.<\/p>\nRTO – Recovery Time Objective<\/h2>\n
RTO is the maximum targeted value for the Recovery Time. <\/i><\/b><\/p>\n
The common\u00a0definition from the\u00a0<\/span>Wikipedia<\/span><\/a> without using RT definition:<\/span><\/p>\n
- \n
- data system is \u201con service\u201d, is ON,<\/li>\n
- disaster occurs and the system is now \u201cout of service\u201d, is OFF,<\/li>\n
- recovery is started by\u00a0user’s request or by an automated request,<\/li>\n
- recovery is finished,<\/li>\n
- the system is \u201con service\u201d again, is ON again.<\/li>\n<\/ol>\n<\/p>\n
Often the moment of the disaster<\/i> and start of the recovery<\/i> are considered to start at the same time, but it is not always true.<\/p>\n
Say, a user has accidentally deleted a database, but did not notice it, and only the next day the user discovered the loss and sent to the data center a request for a recovery. In this example, there is a big gap between the moment of the disaster and start of the recovery, so these moments are not the same.<\/p>\n
We consider \u201cRequest for Recovery\u201d and “Start of Recovery” as the same moment because the request here must start the recovery immediately, even if in reality it does not happen.<\/p>\n
Recovery Time and Recovery Point<\/strong><\/h1>\n
In ERT<\/b>, RT<\/b>O, RP<\/b>O abbreviations<\/p>\n
- \n
- RT<\/b> stands for \u2018Recovery Time\u2019, and it is a time interval,<\/li>\n
- RP <\/b>stands for \u2018Recovery Point\u2019, and it means a moment in time.<\/li>\n<\/ul>\n
The RT and RP terms can be used and discussed separately from ERT, RTO, RPO.<\/p>\n
<\/p>\n- \n
- Recovery Time<\/i> is a duration of the recovery process,<\/li>\n
- Recovery Point<\/i> is a point-in-time from which the data system restores the data after the disaster.<\/li>\n<\/ul>\n
Recovery Time<\/h2>\n
RT <\/b>(Recovery Time) is a period of time required for a data center to resume its former condition after a request for recovery.<\/p>\n
Recovery time can be expressed by the formula:<\/p>\n
RT = <time of resuming functioning> – <time of request for recovery><\/p>\n
RT is overall \u2018out of service\u2019 time interval, it can include the time for trying to fix the problem without specific recovery efforts, the recovery itself, testing, and the communication to the users.<\/p>\n
Recovery Point<\/h2>\n
RP <\/b>(Recovery Point) is a point in time from which the data center restores the data after the disaster.<\/p>\n
The RP point in time may be defined in different ways, it can be<\/p>\n
- \n
- some \u201castronomical\u201d time, e.g., 01-JAN-2018 10:11:33<\/i>,<\/li>\n
- measured starting from the moment of the disaster, e.g., \u201c6 seconds before the disaster<\/i>\u201d.<\/li>\n<\/ul>\n
\u201cAstronomical\u201d time RP is used when considering data unavailability.<\/strong><\/p>\n
The duration of data unavailability time interval can be expressed here by the formula:
\n<data unavailability time> = <time of resuming functioning> – RP<\/p>\n\u201cBefore the disaster\u201d approach of defining RP is used when considering a data loss.<\/strong><\/p>\n
The duration of lost data time interval can be expressed here by the formula:
\n<lost data time> = RP<\/p>\nERT, RTO & RPO\u00a0Definitions<\/h1>\n
Usually ERT, RTO, RPO are defined without using definitions of RT and RP, but they can be used.<\/p>\n
ERT – Estimated Recovery Time<\/strong>\u00a0<\/span><\/h2>\n
ERT is the estimated Recovery Time.<\/strong><\/em><\/p>\n
The common definition<\/a> without using RT definition:<\/p>\n
The estimated duration for the database to be fully functional after a restore\/failover request<\/em>.<\/p>\n
RTO – Recovery Time Objective<\/h2>\n
RTO is the maximum targeted value for the Recovery Time. <\/i><\/b><\/p>\n
The common\u00a0definition from the\u00a0<\/span>Wikipedia<\/span><\/a> without using RT definition:<\/span><\/p>\n
- measured starting from the moment of the disaster, e.g., \u201c6 seconds before the disaster<\/i>\u201d.<\/li>\n<\/ul>\n
- Recovery Point<\/i> is a point-in-time from which the data system restores the data after the disaster.<\/li>\n<\/ul>\n
- RP <\/b>stands for \u2018Recovery Point\u2019, and it means a moment in time.<\/li>\n<\/ul>\n
- RT<\/b> stands for \u2018Recovery Time\u2019, and it is a time interval,<\/li>\n