In any storage system, the one feature that is of paramount importance to the user is data protection. Along with the idea that data will not be lost due to a system crash or a design bug, the administrator and users also expect that a storage system will protect them from inadvertent deletions, unwanted modifications, malicious agents, and the like.
To keep data safe and protected, a wide variety of data backup solutions exists in the storage industry. Perhaps the most common method of data protection is through scheduling data backups at regular intervals, either on the storage system itself, or to tape media. This method is virtually foolproof in terms of the data integrity it provides, but is burdened with the major disadvantages of requiring massive storage capacity, and causing substantial service disruptions during the backup period.
Because server backups have the potential to disrupt operation or drain bandwidth and/or performance, they are often performed overnight or other periods of slow / low server traffic, which can require additional resources outside of normal working hours. Moreover, as a result of these disadvantages, it is typically impossible to schedule backups more frequently than about once a day, causing a potentially large window of data loss if a restore must be made.
In response to the drawbacks involved with simple reliance on daily (or nightly) tape or drive backups, data snapshots are rapidly being adopted as an industry-wide standard for protecting data with increasingly fine granularity. Whether they are captured according to a schedule or under the direction of an administrator, a data snapshot involves the storage system takes point-in time images, or 'snapshots,' of the contents of a volume in a storage system. In a way, each snapshot is similar to an incremental backup of the data within the system. What distinguishes snapshots is the manner in which they back up data, and their positive impact on space utilization and system performance.
The snapshot implementation offered in the StorTrends iTX software by American Megatrends, featured in every StorTrends SAN and NAS appliance, can be considered one of the premier snapshot implementations in the industry. StorTrends provides all of the above features, at a minimum performance premium, with minimal wastage of space, and with almost no performance impact or data degradation. At this time, no other implementation has been able to improve on such phenomenal snapshot performance.
Generally speaking, snapshots look and behave like complete backups – they can be mounted as volumes, read simultaneously without affecting the volume that they represent, rolled back onto the volume if required, and deleted to create free space. Some snapshot implementations also permit writable snapshots, in which snapshots may be modified to create branches of volumes. The ease and flexibility of performing these operations has been instrumental in speeding up the adoption of snapshot technology in the IT industry.
The Advanced Snapshot module featured in StorTrends iTX Data Storage Software enables up to 2,048 snapshots (Read-only and Read-write) at the block or file level. It also allows for rapid creation and deletion of a snapshot, permitting faster, more secure back-ups than ever before. Advanced Snapshot technology is focused on performance, enabling customers to mount, review and instantaneously roll back to a snapshot with near-zero performance degradation.
In addition, the snapshot implementation found in StorTrends iTX is lightweight and flexible, making it easy to add new features and fine-tune existing ones. Moreover, StorTrends iTX uses its snapshot implementation to enable various other attractive features, primary among them being Snapshot Assisted Replication (SAR) and Continuous Data Protection (CDP). StorTrends makes sophisticated snapshot technology that was once available only to enterprise-level users accessible to those in small and medium sized business (SMB) for the first time.
OPERATIONS THAT CAN BE PERFORMED ON SNAPSHOTS
The attractiveness of snapshots as a viable alternative to tape-based backups lies in their versatility and their ability to make other storage-related tasks faster and more convenient.
- SNAPSHOT CREATION: Snapshots may be created in one of two ways. An administrator may decide to create a snapshot schedule, which automatically takes snapshots at predefined intervals of time. When there are a large number of volumes that need to be managed, this is often the only practical option. Most storage management software packages available today offer tremendous flexibility in creating schedules for snapshot creation.
- MOUNTING SNAPSHOT VOLUMES: In order to read from a snapshot volume, it is necessary to mount a snapshot as a read-only volume. For example, if a user has accidentally deleted a file, it may be required to mount a previous snapshot and recover the file. Sometimes, it may be necessary to mount multiple snapshots simultaneously, compare the contents of a particular file, and choose the one that is closest to the point of loss to copy back to the original volume.
- SNAPSHOT DELETION: In order to recover storage capacity, administrators must routinely delete old snapshots. This is often part of a snapshot schedule, and as a working rule, the oldest snapshot is deleted prior to the creation of a new snapshot. Sometimes, however, administrators may choose a different strategy for snapshot deletion. For example, if a volume has not changed substantially between two earlier snapshots, but has changed dramatically between two later ones, the administrator may prefer to delete one from the first pair rather than one of the second.
- SNAPSHOT ROLLBACK: When data has become irretrievably corrupt (due to a virus, for example), or has been destroyed entirely (i.e., if a disk is accidentally formatted, or the like), the administrator has no choice but to perform a "rollback" from a snapshot onto the volume. In a rollback operation, the administrator has the ability to essentially select a snapshot from a list of those currently available and rewrite it to the target, so as to replace the entire contents of the volume.
- WRITABLE SNAPSHOTS: The more advanced snapshot implementations available in the market today, such as the snapshot module featured in StorTrends iTX, allow snapshot volumes to be mounted as both read-only as well as read-write volumes. When a snapshot is capable of being mounted as read-write, it is called a writable snapshot.
SNAPSHOTS AND DATA REPLICATION FEATURES
As snapshot technology has evolved and grown more mature and stable, several vendors have discovered ways of leveraging the power of snapshots to make other storage-related tasks faster, more convenient, and consequently, more reliable.
Volume replication is an increasingly important and sought-after feature in storage systems that protect valuable data. One of the most important criteria that govern the replication algorithms underpinning replication technology is the consistency of data at any replication point. Since applications like Oracle® using a volume may write data in a certain order, failure to adhere to that order may render data unusable if the replication process is performed at an inconsistent point. This issue is known as write-order fidelity, and is a major consideration in replication applications.
Asynchronous replication is often adopted in response to the high bandwidth requirements and distance restrictions of synchronous replication, particularly in cases where primary and secondary storage are separated by considerable geographical distance. Asynchronous replication can minimize the performance impact and bandwidth requirements of synchronous replication by forgoing the need to write to the primary and secondary simultaneously.
Because of the absence of a "hold" on recording the application write, application performance is improved, as I/Os can be recorded faster. In many cases, reduced bandwidth costs can be achieved by leveraging this data lag period. Furthermore, replication can be executed over greater distances because the time/write constraint has been eliminated.
Snapshot Assisted Replication (SAR)
StorTrends iTX makes use of its advanced data snapshot capability to offer a unique form of Asynchronous Replication that uses data snapshots to perform the replication activity, known as Snapshot Assisted Replication (SAR). SAR allows for the chronological replication of snapshots on a remote machine, with the ability to organize by application based consistency groups. In failover to a secondary appliance, StorTrends iTX will automatically rollback to the latest consistent snapshot.
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