Drive sharing

Since the backup servers are presented with dedicated virtual drives and libraries from the front end of Storage Director, the physical drives are “decoupled” from the backup servers and managed by the Storage Director. Therefore, when the data from the disk cache is copied to the physical tape, a physical drive is dynamically allocated for that purpose without respect to what backup server originated the data. This capability takes drive sharing to a new level. Now you can effectively share all the drives in the library with multiple backup servers and multiple backup applications.

Library sharing

Storage Director can easily make one SCSI-controlled library look like many virtual libraries. This “virtual partitioning” of a device allows it to be shared among multiple servers, whereas the single, physical device would not normally be available for sharing. Although some larger libraries are able to partition a library in a similar manner, smaller libraries generally do not, so the Storage Director could bring that capability to all libraries.

Library consolidation

Storage Director can also consolidate many small libraries or auto-changers into one larger library for a backup server. This “virtual consolidation” eases library management for the backup application.

Performance

Storage Director comes with several performance benefits:

• Instantaneous mounts - Mounts are all instantaneous to the backup application since they are virtual mounts; therefore the mount wait time is basically zero.
• Faster than a tape drive - Data can be accepted at up to wire speed. For a 4Gb FC port with a single virtual drive, that means over 300MB/sec/FC port, which is faster than any single, physical drive performance. With Storage Director, the bottleneck has now moved from tape to the backup server.
• Increased physical drive performance - Because Storage Director stages the backup data onto a disk cache (InfiniCache) first, the data transfer from disk to tape may be done in larger bursts, thus providing for better utilization and performance of the physical tape drive. We have seen up to a 4X improvement in physical drive performance with Storage Director, which can lead to more bandwidth capability or cost savings in the number of drives needed.

Reduced cost and improved reliability

The number of physical drives required for a backup environment is determined by two primary factors: connectivity and performance.

Storage Director handles connectivity requirements with virtual drives and libraries, so the need for a specific number of physical drives is totally eliminated.

The performance requirement is no longer tied to a backup window, since Storage Director's front end and InfiniCache (disk cache) provide more than adequate speed. You can then copy the data to physical tape within 24 hours or in the time between backups.

Backing up initially to Storage Director's InfiniCache usually reduces the number of physical drives required in the system—which translates to a reduction in cost and improvement in the overall reliability of the tape library. For example, the backup system “thinks” that it has 12 tape drives, but in reality it only has four. Compare the reliability of a system with 12 real drives to a system with Storage Director and four real drives: there is a perceived improvement in reliability for the given 12 drives.

Greater resilience

When a backup occurs, a tape gets mounted and then the data is written to tape. As with any electro-mechanical device, sometimes errors occur. A tape won’t mount or dismount, or errors may occur during the write operation, causing the backup to fail.

With Storage Director, the backup actually occurs from the backup server to the InfiniCache, which is much less likely to fail; therefore, the success rate is much higher.

If a physical tape failure occurs when Storage Director tries to write the data to tape, it would merely try to mount the tape on a different drive and try again. If for some reason Storage Director could not successfully send the data to tape, the data would stay in the cache until the tape problem was fixed. This method of data protection allows time for the problem to be resolved without affecting the backup application. The amount of time that is allowed to fix the problem depends on the size of the cache, but the minimum would be 24 hours, which is the presumed time between daily backups.

This is another way in which Storage Director can make the library appear to be more reliable and available.

Additional functionality

Storage Director has many features and functions that can enhance a physical library. As an example, Storage Director’s Bulk Eject feature enables the application to eject tapes out of the virtual library one at a time while they are not ejected out of the physical library until the operator is ready to remove them. The operator can select a group of tapes to be ejected at the same time and fill up the cartridge access port (CAP) or the import/export slots of the physical library. Then those tapes may be removed from the physical library all at once.

Improved library connectivity

Since Storage Director has iSCSI capability on the front-end (host) interfaces, it now adds that connection method to the interfaces that may be used to the library and drives. For example, in low-end configurations, iSCSI connections could be used in place of parallel SCSI for both the changer and the drives. In higher-end configurations, iSCSI could be used for the changer interface and Fibre Channel could be used for the tape drive interfaces to meet the need for higher performance. As new interface technologies such as 10Gb iSCSI or 8Gb FC become available on Storage Director, the overall tape subsystem will be enhanced automatically. 

These faster interfaces, along with disk cache technology, can greatly improve the perceived performance of the tape subsystem, even if the performance of the physical tape interfaces and drives are a lot lower, since those back-end operations to physical tape are done in the background.

Common device drivers/reduced host maintenance

One of the big complaints with tape is that every time a new tape drive or library comes out, new device drivers need to be developed for the various operating systems and applications, which require updates to the backup servers so they can support the new technology.

Storage Director lets you present a common tape drive image, such as LTO-1, to the backup application, and at the same time change the capacity of the virtual tape to be equal to that of the physical tape. In other words, if there were LTO-4 drives on the back end, the front end could present LTO-1 drives with 800GB native capacity. This capability allows for new tape technology to be introduced without the need to change all the drivers on the backup servers. Storage Director knows how to communicate with new tape devices.

The same would be true for libraries as well. Where a specific library type might not be supported by a backup application, Storage Director can present a library type that is supported. For example, Storage Director could make an ACSLS-controlled library look like a SCSI-controlled library for an application that does not support ACSLS.

Leveraging all library functionality

Generally, backup applications tend to degrade library functionality to some common point so they can treat all makes and models of tape libraries in the same way. The primary concern is application functionality and not to make any particular tape library product look good, unless it is their own. Therefore, backup applications usually do not take advantage of any unique functionality that may be present in some library models.

On the other hand, Storage Director works closely with library manufacturers to learn about any unique functions. Those functions can be adopted into Storage Director so that all customers, regardless of the backup applications they are using, can benefit from all library capabilities. In this way, Storage Director is focused on tape management and connectivity, making it more robust than typical backup technology.