Published: 09 Sep 2005
Cisco's switch-based backup
Cisco Systems inc. recently announced its Fibre Channel (FC) MDS 9000 Storage Services Module (SSM) and SAN-OS 2.1 software--which includes support for Xcopy, or Extended Copy--to enable Network Accelerated Serverless Backup (NASB). With serverless backup, the server is removed from the backup process so it doesn't become a performance and reliability bottleneck.
Xcopy has been around for quite a while and is part of the SCSI command set, intended to enable copying data from one storage device to another without passing the data through a server. The notion of serverless backup is attractive because it offers faster backup speeds, lower server loads and less LAN traffic. Still, Xcopy hasn't been widely embraced by users. Users found that without backup software support, serverless backup had many problems that Xcopy didn't address (and still doesn't).
What Cisco has done that's different from the Xcopy support built into other storage products is to make deals with backup software vendors to support their hardware, so the backup software has access to the Xcopy protocols through Cisco's MDS 9000. Users still have to run their backup software, but it connects to the Cisco hardware and bypasses the server. However, Cisco's Xcopy approach isn't necessarily unique: EMC Corp. offers backup apps within its proprietary hardware/software that use Xcopy to the same effect, and other vendors--such as Advanced Digital Information Corporation (ADIC) and its Pathlight VX series and Crossroads System Inc.'s Network Storage Controller--offer products that are similar to serverless backup, but aren't based on Xcopy.
|Different ways to move copied data|
Different ways to copy
In the traditional definition of serverless backup, the application server doesn't process data; it's moved directly from storage to backup from an FC storage array to an FC or SCSI backup device. The problem is that the backup application's ability to handle errors, as well as issues like tape changing in libraries, can't be handled through the Xcopy protocol.
Making a fast, block-by-block copy of a volume is useful, but not the only desirable backup strategy. Because Xcopy operates at the device level--it needs to be available in only one device on the SAN (switch or array)--passing blocks from one device to another, it isn't easy to make backup software aware of the Xcopy process. This means that each vendor must come up with its own method of supporting Xcopy.
Today, serverless backup is viewed as less of a panacea than it was a few years ago because replication-based backup is better for many apps. W. Curtis Preston, vice president of services development at Framingham, MA-based GlassHouse Technologies, says he knows of only a handful of companies that use Xcopy for serverless backup--most use replication.
However, Preston is a fan of serverless backup under certain circumstances. For instance, backing up a large database can be hard on the database server, so serverless backup may be the only way to make backups run faster. He also likes the idea of combining Xcopy with virtual tape libraries (VTLs) to copy data from disk to tape inside the virtual tape library. This can be done with existing systems, but the backup software isn't aware of the copy being made. If Xcopy was implemented in a VTL, a backup application would be aware of Xcopy and be able to use it intelligently.
|Pros and cons of various data copy methods|
Cisco's Xcopy implementation
Cisco integrated Xcopy onto its line card--the Storage Services Module (SSM)--that supports 32 FC ports and includes an embedded virtualization engine that provides Xcopy functions and talks to backup applications. The Xcopy implementation is highly available, highly integrated and delivers speeds up to 16Gb/sec per line card.
Cisco has cemented partnerships with CommVault Systems Inc. and Computer Associates (CA) International Inc. for their backup products--Galaxy Backup & Recovery and BrightStor Enterprise Backup, respectively--to support the MDS 9000; Veritas Software Corp.'s NetBackup support is in the works. Each line card has eight data mover modules, and each data mover can support 2Gb/sec of serverless backup. Backup applications can load balance across multiple cards for high availability. The storage and backup devices don't have to be directly connected to the SSM line card; they can be connected to any port on the MDS. The card can load balance eight devices and support multiple jobs on each data mover.
The bottom-line value of MDS with Xcopy is that it allows storage managers to use their existing backup software (as long as it's CA, CommVault or Veritas) to manage serverless backups. There are many vendors that offer disk-to-disk backup products, as well as a number of FC switch vendors such as Maxxan Systems Inc. and McData Corp., and storage router vendors such as Crossroads, NeoPath Networks Inc. and Network Executive Software that put intelligence in the switch/router to enable virtualization, replication and snapshots. These products can all provide replication of a volume or create snapshots that have a minimal impact on the application server or availability of data, thereby providing many of the same benefits as serverless backup in general.
Indeed, some of these products may offer greater flexibility than what is currently available with Cisco MDS because snapshots or data mirroring can be used with whatever backup software your company has standardized on. Some of these backup processes, such as remote replication, can run on iSCSI over a standard WAN connection, eliminating the need for costly dark-fibre leases.
Reduce backup overhead
There are many alternatives available to create serverless backups, or to at least offload the overhead of backups from a primary application server. Deciding whether to use Xcopy or some other data copy method will depend on many factors, including the size of the data to be protected, the number of application servers to be protected, available bandwidth, whether the backups need to be at the same site or a different one, and your budget.
With prices starting at more than $100,000, intelligent switches aren't a fit for a single application server. For enterprises with many application servers to protect and limited backup windows, the Cisco MDS 9000 offers high speeds, scalability and wide compatibility. Smaller organizations should look into storage routers and storage virtualization products, which can offer some of the same advantages at a lower cost and speed.