Move your backups to a SAN

Speed, communication and block-orientation are just a few of the reasons that users are moving their backups from Ethernet-based LANs to Fibre Channel SANs.

What you will learn from this tip: Speed, communication and block-orientation are just a few of the reasons that users are moving their backups from Ethernet-based LANs to Fibre Channel SANs.

With the growing availability of native Fibre Channel (FC) backup devices -- such as tape drives -- and the ever shrinking backup window, moving backups from Ethernet-based LANs to FC SANs is becoming increasingly attractive for midsized and large organizations.

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One reason for the attraction is the growing availability of backup devices that communicate directly in FC protocol instead of going through a layer to translate to SCSI protocol. SCSI is more common, of course, and the translation approach allows you to continue to use existing SCSI equipment, but it can create a bottleneck in throughput. In addition, vendors like StorageTek offer even more advanced features directly built into backup devices, eliminating the need for routers or bridges to sit between the backup device and the SAN. The changes in the technology help accentuate the advantages of backing up over a SAN.

The major advantage of moving your backups from the LAN to a FC SAN is speed. FC SANs start at 1 gigabit per second (Gbps), with 2 Gbps speeds common and interoperable 4 Gbps available at very little additional cost to 2 Gbps SANs. This provides rawer throughput than the typical LAN.

However, that is only one of the SAN's speed advantages. Backing up over a SAN makes more efficient use of resources such as bandwidth. This is because the data being backed up is more uniform than run-of-the-mill LAN traffic and the SAN is tuned for that traffic. Further, SANs are typically block-oriented systems rather than file-oriented. This means that the SAN is dealing with data in standard-sized chunks, which adds more uniformity to the process. Also, LAN traffic is inherently bursty and LANs have to be set up for that. SANs are designed to handle constant high transfer rates, which are a much better match for the continuous maximum-speed transfers involved in backups.

The drawbacks to switching from Ethernet to FC SAN for backups are cost and complexity. FC equipment is significantly more expensive than Ethernet equipment, at least at common Ethernet speeds. In addition, a FC SAN is more complex than an Ethernet LAN. However, in most cases the SAN isn't installed simply for backup, which lowers the effective cost of the SAN. This is especially true since FC SANs tend to be rather granular and it may take little, if any, additional investment in a FC network to support backups.

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About the author: About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years, he has been a freelance writer specializing in storage and other computer issues.


This was first published in March 2006

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