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Backup Lag Time

Backup lag time is the time taken between the time the data is changed and the time the backup completes.

This is an important factor in asynchronous backup methods.

Lower lag time means less data is lost.

Lag time can depend on a number of factors which are covered below.

Timing Method (replication, or periodical)

  • replication can be used to back up data as soon as it is changed, as long as that is possible
  • periodical backups take place at a regular interval

Periodical Backup Frequency

  • such as every 5 minutes, or every 24 hours

Backup Method (mirrored, differential or snapshot)

  • differential backups are performed on new/changed data only, increasing backup speed, and decreasing restore time. Lag time will be low.
  • snapshot backups are a full backup from the start of the data to the end, they are usually very slow, but are easier and faster to restore. Lag time will be high.
  • mirrored backups are a type of differential backup, which keeps two data stores in sync with each other, at the cost of extra processing requirements. For example: a secondary database, always running, and ready to take over the functionality of the primary database. Lag time will be low.

Near-Live Backup Location (local or remote)

  • with a local device, data can be transmitted and stored quickly and reliably, decreasing lag time.
  • with a remote device, data takes longer to transmit, and is more in danger of factors such as network issues between the devices, increasing lag time but adding protection of near-live backup data in case of physical destruction of the primary data source.

Load and Network Conditions

  • systems under load will perform backups slower
  • network conditions between remote backup devices increase lag time

Backup System Problems and Outages

  • with asynchronous backups, outages in backup software, hardware or networks can go unnoticed unless appropriate monitoring and procedures are in place
  • this can increase backup lag time dramatically, or temporarily disable backups completely

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