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Do you trust your backups? Read More

Replication Mode

The selection between synchronous or asynchronous mode is made according to the RPO/RTO ratio (described in the following paragraph), the distance and the level of availability desired. The quality of link between the sites should also be considered.

Tolerance / Criticality of the Application Data Protection strategy
RTO more than or equal to 72 hours Restoration from backups on tape
RTO less than 24 hours Restoration from a remote site, asynchronous replication
nul RPO / minimum RTO Restoration from a remote site, synchronous replication
nul RPO/ metropolitan distance Synchronous replication
nul RPO / departmental distance Synchronous replication between both departmental sites and asynchronous replication between departmental sites and non-departmental sites

The replication technologies can be applied at the storage level; replication is performed between two remote disk arrays connected through Fiber Channel (FC) technology, but it is also possible to perform a data replication through conventional TCP/IP network.

  • Mirroring or Cloning

In synchonous mode, this technology provides an identical copy of the production volume, it is generally used for disaster recovery on another site, for tests or backup on a remote server executed from production data.

Read More... Clustering

Point-In-Time-Copy

This technology is commonly known as Snapshot and is often associated with a backup application, if possible to a remote site from where the data have been replicated. From the moment the snapshot has been created, original data are copied into the snapshot volume before being modified on the production volume. The snapshot volume is progressively filled as well as writing operations are generated on the production volume until it is filled or destroyed. The application reads and writes seamlessly on the volume of production, the backup application has a read-only acces to the volume of data containing the original data. It may be possible to keep snapshot online to accelerate the restoration process which can be slow depending on the relevance of data to restore.

Read More... Real Time Copy

Level of Availability

The level of availability can be expressed by the Nine Rule :

Percentage of availability Percentage of unavailability Annual unavailability Weekly unavailability
98% 2% 7.3 days 3 hours, 22 minutes
99% 1% 3.65 days 1 hour, 41 minutes
99.8% 0.2% 7 hours, 13 minutes 20 minutes, 10 secondes
99.9% 0.1% 8 hours, 45 minutes 10 minutes, 5 secondes
99.99% 0.01% 52.5 minutes 1 minute
99.999% 0.001% 5.25 minutes 6 secondes
99,9999% 0,0001% 31,5 seconds 0,6 secondes

The effect of service unavailability time can be more or less important according to the business and the day this happens. In most environments, the transition from a system availability of 99% to 99.9% increases the costs by 5 to 10 times.

Lire la suite... Technologies

Recovery Point Objective

( RPO) This indicates the number of days, hours and minutes of production data which the business is ready to give up further to an incident.

Recovery Point Objective

The technologies implemented in the framework of backup and archiving lead to define an RPO not so similar from the version of data production at the time of the incident. Following the need expressed by the restoration, the set of replication technologies until archiving allow to make available a set of versions of data to restore.

It is thus essential to define highly available systems which guarantee RPO expected by the company.
Read More... Degraded Operation Interval