NAS/Tape Backup Strategies Cope With New Data Cornucopia.
So with all this great data residing on NAS devices, backup procedures are critical. Lower-end NAS devices can simply and easily back up to a simple tape drive. But midrange and high-end appliances storing gigabytes and terabytes of data require sophisticated backup approaches such as tape libraries. In addition, many administrators want to take NAS backup routines off the LAN without having to separately maintain NAS backup procedures. Steve Bishop, CTO of WorldStor, agrees: "The real key is instead of developing a backup solution around your NAS, you want to include your NAS into the enterprise backup function you already have." There are several alternatives to consider when using a NAS and tape library for backup: use the tape library as direct-attached storage, use the NAS itself as a LAN-free backup device, or backup to a library over a SAN.
Backing Up The NAS
A common backup method is to attach tape libraries directly to the NAS. This is the strategy that Storage Service Providers often follow in their data centers. SSP WorldStor uses a number of high capacity NAS devices within their infrastructure, including EMC Celerra's. They back them up to tape libraries using an NDMP-compliant program from VERITAS that manages the library while providing a link directly to the NAS device.
Some vendors have attempted to market a LAN-based product for NAS backup with integrated intelligence and backup software. The products have met with only limited success. Steve Richardson, vice president of marketing at Overland, believes they did not do well because the backup applications were not LAN-free and added an unnecessary level of complexity into the backup routine. Instead, Richardson suggests backing up the NAS as part of an overall backup strategy, including using the same backup management software already used throughout the network.
Richardson pointed out that the issue is not offering NAS-only tape libraries, but providing connectivity between the two. This enables the possibility of LAN-free backup, an important function of storage systems and their backup devices. In Overland's case, they partnered with Network Appliance using a Fibre Channel connection with a filer and tape library using NDMP. Using a standard backup application, they were able to run a LAN-free backup to the library.
Using HAS As A Backup System
IT administrators can reduce backup times by streaming data from the disk volumes to tape devices attached to the NAS server. This approach permits the tape devices to run at their streaming speed, avoiding the stop/start cycles of the tape transport that often impacts throughput. NDMP enables the NAS appliance to fulfill backup and restore commands locally for high performance, yet operate under the control of an NDMP-compliant backup program.
Such NAS appliances sometimes bear more of a resemblance to archive servers than file servers do. One such product is Grau Data's Infinistore Virtual disk system, which president Mike Holland describes as "a tape library with a server in it." The Infinistore is a self-contained disk system including a server with data management software, RAID disks for data caching, and Sony AIT tape drives and media. During backup, data is written into the disk cache and eventually migrated down to tape media. Since the most active data usually remains in the disk cache, restores are often disk-based.
The advantage of using network-attached tape subsystems for online storage is that the users can recognize data by filenames instead of tape volume. This is a definite plus to a user looking at a restore operation. In fact, Holland takes on a faintly conspiratorial tone when discussing storage consolidation using SANs instead of lower-priced NAS appliances. "Big disk drive guys can't continue to move big iron unless they have a server consolidation strategy going on in the customer environment," he notes. Meanwhile, the cost of midrange NAS devices is considerably less, and management is simpler. "The skill sets don't exist to aggressively manage data," he adds. "The user community is unwilling to manage data, the operations folks are unable to manage it, so data just continues to accumulate on high capacity storage devices. EMC is very happy to see that continue, as is NerApp and a few others."
Backing Up The HAS Through The SAN
Conspiracies aside, backing up the NAS through the SAN can be a good approach to the problem of managing multiple NAS appliances. (NAS solutions are not known for their scalability, precisely because it's difficult to integrate the appliances.) Spectra Logic recently demonstrated a SAN-based backup architecture for Network Appliance filer environments by utilizing its Fibre Channel-based tape libraries, a Vixel Fibre Channel switch, and storage management software from VERITAS and Legato. The Ethernet-enabled filer was connected to the SAN via the switch, the switch was connected to a tape library, and in separate trials the VERITAS and Legato software managed the backup from the NAS to the tape library via the switch. The backup did not impact the Ethernet network or the network server.
This approach, for example, allows multiple NetApp filer customers to take advantage of a more cost-effective and manageable backup strategy than was previously available. Utilizing the SAN-based approach, users can build a backup architecture that can be scaled as the number and capacity of their filer pool grows.
WorldStor had added an automatic alert system for storage capacity, including its NAS devices. When a NAS file system is close to capacity, the system alerts the network center and the problem enters a trouble ticketing system. Bishop adds, "That's the way the high-end shops are doing it. The NDMP products from the major players are getting better and better at tape sharing through storage area networks. There's also some movement towards doing hot backup from the NAS device by leveraging SAN technology like snapshot within the NAS environment."
Of course, these kinds of backup strategies are enormously useful but quite complex. As Holland puts it, "Magnetic tape as a storage medium can be employed in a network-attached environment. Providing you take care of a bunch of other issues."
Amen to that.
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|Title Annotation:||Industry Trend or Event|
|Publication:||Computer Technology Review|
|Date:||Feb 1, 2001|
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