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Ask SQLTeam Question

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Posted - 10/02/2001 :  10:08:53  Show Profile  Visit AskSQLTeam's Homepage
Andrew writes "What's the real deal with SAN vs. NAS?

We have a large database (many tables, millions of rows, 700+GB) that we may be implementing in SQL Server 7

We're looking at SAN solutions from EMC and NAS solutions from Network Appliance.

Network Appliance make great play of the fact they are the only MS-approved NAS vendor for SQL Server.

EMC state you should never put SQL Server data on a NAS.

Clearly, both are biassed ;)

For their part, Network Appliance hint that there are some limitations in support but neither their site nor MS's detail what they may be.

Can you tell me the real differences and limitations?
Should I go NAS or SAN?

Given that the databases are used as a web back-end with approx 9 million hits/day (4-6 SQL Servers, multiple front-end boxes), will I really notice the difference between SAN's Fiber Channel link vs. Gig-E on the Network Appliance? (Yes, I know this is kind of like asking how long a piece of string is, but you know how it goes ;)"

Official SQLTeam Chef

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Posted - 10/02/2001 :  10:43:48  Show Profile  Visit RocketScientist's Homepage
Let me start by saying that we've got a Network Appliance filer (two of them, actually, clustered) and a Compaq TaskSmart N2400 (a signficiantly less expensive device that fills the same need, without the clustering). These are both great products. We're extremely happy with our network attached storage solutions for our application.

That said, there are some fairly serious limitations to using a NAS for SQL Server. All SQL Server knows about storage is that it's talking to a filesystem. It doesn't really understand that the filesystem is on a network device. SQL Server is tuned to deal with local filesystems. So, when you use a network device as a filesystem, the entire system has to respond nearly as quickly as a local filesystem. That means the network controller on the SQL Server, any switches or other network infrastructure, the NAS device, and the disks on the NAS device.

The biggest problem we've had has been latency on the SQL Server's NIC. To solve that we use dual-port NIC's in a Fast EtherChannel configuration. This provides two pipes for the server to use, and reduces latency enough that SQL Server doesn't notice. It also makes backups and file copies for that machine just FLY. :)

The second biggest problem we've had is that there doesn't seem to be nearly the quality and attention to detail in network infrastructure that there is in disk hardware. Go pick up a Cat5 patch cable and a SCSI cable and compare the relative quality. Of course, the SCSI cable probably cost you about 100 times more than the network cable, but it's also a much higher quality cable with a more robust connector.

Bear in mind that a NAS solution is going to fundamentally be extending the SCSI (or FibreChannel, whatever) bus of your server across your network, so your network needs to be as robust and bulletproof as those solutions. Consider armor-plating your network cables :). Seriously, a NAS is close to the tolerance limit for a network with respect to reliability, dont' cut any corners. Get an excellent, carrier class switch and don't skimp on patch cables.

All that said, I'd like to make the humble suggestion that you have a discussion with your Compaq rep on their StorageWorks products. These are high-availability SAN's at a fraction of the price of EMC. We had EMC in for a dog-and-pony show before we bought our TaskSmart. We were considering a bigger strategic move to centralize storage and backup. After the post-sticker-shock-heart-attack, we decided on the Compaq strategy. The StorageWorks stuff all comes from the acquisition of DEC that Compaq made a few years back, and it's good equipment.

As expensive as the Network Appliance stuff is, the EMC guys make it look like you're buying a bunch of tinfoil.


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