One commonly raised objection to the use of snapshots as a data protection strategy is the fact that the "real" data and the snapshot data are located on the same drives. Loss of those drives would result in the loss of both the primary data and the backup.

This is a valid concern. Local snapshots are used for day-to-day backup and recovery needs, and in that respect the snapshot is a backup. Close to 99% of all recovery scenarios in NetApp environments rely on snapshots to meet even the most aggressive RTO requirements.

Local snapshots should, however, never be the only backup strategy, which is why NetApp offers technology such as SnapMirror replication to quickly and efficiently replicate snapshots to an independent set of drives. In a properly architected solution with snapshots plus snapshot replication, the use of tape can be minimized to perhaps a quarterly archive or eliminated entirely.

A consistency group backup involves capturing the state of a dataset (or multiple datasets) at a single atomic point in time. As a database example, this includes all database components, such as datafiles, log files, and other files directly associated with the database. This works with almost all relational database products, including Oracle RDBMS, Microsoft SQL Server, SAP HANA, PostgreSQL, MySQL, and MariaDB. Protecting a VMware configuration with a consistency group backup would be similar - capturing all of the datastores and potentially the ESX boot LUNs in a single atomic point in time.

Creation of a such a consistency group snapshot is essentially simulating a crash, which is why such backups are frequently called crash-consistent backups. There are sometimes concerns with support for recovery scenarios, but it is important to understand that no recovery procedure is usually required. When the application starts up after restoring a consistency group backup, it performs the usual log recovery processes, file system journal replays, and other tasks to replay any I/O that was in-flight at the point of the backup. The application then starts as usual.

Essentially, any application that can withstand a power failure or server crash without data corruption can be protected in this way. The fact that this works can also be demonstrated by the huge number of applications protected with synchronous and asynchronous mirroring products from many different vendors. If a disaster suddenly strikes the primary site, then the replica site contains a consistent image of the original environment at the moment the disaster occurred. Once again, no special recovery procedure is required.

The RPO for this approach is usually limited to the point of the backup. As a general rule, the minimum RPO for single-volume snapshots is one hour. For example, 48 hourly snapshots plus another 30 days of nightly snapshots is reasonable and would not require the retention of an excessive number of snapshots. An RPO lower than one hour becomes more difficult to achieve and it is not recommended without first consulting NetApp Professional Services to understand the environment, scale, and data protection requirements.

The RTO can usually be measured in seconds. A an application is shut down, the volumes are restored, and the application is restarted.

The simplest approach is to place all the files or LUNs in a single volume consistency group, which allows a snapshot creation to be scheduled directly in ONTAP. Where a dataset must span volumes, a consistency group snapshot (cg-snapshot) is required. This can be configured using System Manager or RESTful API calls, plus SnapCenter is capable of creating a simple consistency group snapshot on a defined list of volumes.

This section addresses remote data protection, for which data is replicated to a remote site for the purposes of secure offsite storage and disaster recovery. Note that these tables do not address synchronous mirroring data protection. For this requirement, see the NetApp MetroCluster documentation including MetroCluster and SnapMirror active sync

The DR RPO is limited by the available network bandwidth and the total size of the data being protected. After the initial baseline transfer is created, the updates are only based on the changed data, which typically is a low percentage of the total data footprint, although exceptions do exist.

For example, a 10TB database with a 10% weekly change rate averages approximately 6GB per hour of total changes. With 10Gb of connectivity, this database requires approximately six minutes to transfer. The change rate varies with fluctuation in the database change rate, but overall a 15-minute update interval and thus a 15-minute RPO should be achievable. If there are 100 such databases, then 600 minutes is required to transfer the data. Therefore, an RPO of one-hour is not possible. Likewise, a replica of a single database 100TB in size with a 10% weekly change rate cannot be updated reliably in one hour.

Additional factors can affect replication, such as replication overhead and limitations on the number of concurrent replication operations. However, overall planning for a single-volume replication strategy can be based on available bandwidth, and a replication RPO of one hour is generally achievable. An RPO lower than one hour becomes more difficult to achieve and should only be performed after consulting NetApp Professional Services. In some cases, 15 minutes is feasible with very good site-to-site network connectivity. However, overall, when an RPO below one hour is required, the multi-volume log replay architecture yields better results.

The RTO with consistency group replication in a disaster recovery scenario is excellent, typically measured in seconds from a storage point of view. The most straightforward approach is to simply break the mirror, and the database is ready to be started. Database startup time is typically about 10 seconds, but very large databases with a lot of logged transactions could take a few minutes.

The more important factor in determining RTO is not the storage system but rather the application and the host operating system upon which it runs. For example, the replicated data can be made available in a second or two, but this only represents the data. There must also be a correctly configured operating system with application binaries that is available to use the data.

In some cases, customers have prepared disaster recovery instances ahead of time with the storage prediscovered on operating systems. In these cases, activating the disaster recovery scenario can require nothing more than breaking a mirror and starting the application. In other cases, the OS and associated applications might be mirrored alongside the database as an ESX virtual machine disk (VMDK). In these cases, the RPO is determined by how much a customer has invested in automation to quickly boot the VMDK so that the applications can be started.

The retention time is controlled in part by the snapshot limit. For example, volumes in ONTAP have a limit of 1024 snapshots. In some cases, customers have multiplexed replication to increase the limit. For example, if 2000 days of backups are required, a source can be replicated to two volumes with updates occurring on alternate days. This requires an increase in the initial space required, but it still represents a much more efficient approach than a traditional backup system, which involves multiple full backups.