Ask the Expert

Which way to go, the SAN/NAS option

Randy,

I'm having trouble deciding which option is right for me. I currently back up two 1/3 TB of data company wide to tape. Diffs are taking an average of six hours now and I am looking for a solution.

I have read many articles about on the SAN vs. NAS debate but I'm not sure which to go with. What formula do you suggest I go with?

Thanks.


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As with most answers, it depends. I assume you're talking about backup options but you could also consider SAN or NAS for primary storage and then the backup situation as well. For primary storage, the big issue is what are the requirements for your application. Performance is one of the big issues and whether you are doing raw I/O (for databases usually) is another. Sometimes, some applications such as video, satellite data collection, etc. have guaranteed bandwidth requirements. NAS with its remote file access over Ethernet networks may satisfy your requirements but SANs with block I/O and predictable bandwidth may satisfy other requirements. The choice must be made based on your requirements and is not a simple answer.

For backup, you can either backup to a NAS device from a NAS device or from a SAN or direct attached storage device if you're using file-based I/O. You can backup to a SAN device from another SAN device as well for file I/O or block level I/O. In these cases, you have a quick backup and, more importantly, a short restore time in the case of inadvertent data loss.

What many of the enterprise data center storage professionals are doing is taking a point-in-time copy of data (usually a snapshot) on a periodic basis based on business requirements and then backing up that copy to tape on another periodic cycle, again based on business requirements. This solves several problems in that there is minimal disruption when the backup is done since it is a snapshot to disk, time to recovery of data is a business issue (very critical) and is very fast with a snapshot restore or rollback, and the backup storage devices can be less expensive devices (maybe less performance for example). Certainly, you may use more SAN or NAS storage but the business value far outweighs that cost.

So, there's no simple answer. Look at your requirements and determine which fits best. Usually, very high performance environments would use block I/O and would lead you to a SAN while less stringent requirements with a different degree of administration and security would lead you to a NAS device. For backup, there are several solutions that will work.

Randy Kerns
Evaluator Group, Inc.

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This was first published in December 2001

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