Choosing the right switch for storage

By Mark Sutton Monday, 16th March 2009

Storage over Ethernet is a hot topic in the web hosting datacentre at the moment. With several excellent storage protocols to choose from and plenty of vendors offering product there is certainly a lot of choice in the marketplace. But it’s easy to overlook the importance of the Ethernet switches that are going to be carrying your data – after all you just spent a fortune on ‘redundant’ storage right?

What features do I need from a switch?

Most Ethernet storage protocols (think ATAoE, iSCSI, Lustre, NFS) will benefit from a few core features:

Jumbo Frames – enabling jumbo frames will make more efficient use of each packet sent over the network. Look for a capability of 9000 bytes or more.
Flow control – enabling flow control can increase the reliability of your network and reduce packet drops, especially across inter-switch links
10GbE capability – if you have more than a few storage initiators (clients) – each with a GigE link – then it’s relatively easy to run up several Gbit/s worth of traffic across your inter-switch links. Look for 10GbE capability to boost scalability
802.1q VLAN support – OK, so you wouldn’t even consider buying a datacentre switch without 802.1q would you? Good…
Multiple forwarding database – and this might be a bit Procurve-specific – if you are using 802.1q tagged vlans to directly-connected hosts then you’ll need this to stop the switch getting confused over duplicate mac addresses

There are often other gotchas too, for example some features may not play together well. One example is the Procurve 28xx series doesn’t support jumbo frames and flow control being enabled at the same time.

So which switches are good?

Well, historically we have used Procurve for years. It offers a fairly basic set of good features at a decent price. And lifetime warranty too…

The hot models seem to be 2900 if you’re into stackables and if you’re looking for something a bit bigger and modular then the 5406zl comes in quite reasonably around the £3.5k mark.

If your needs are bigger still then you’ll want to look toward the Cisco 6500, Foundry RX and Extreme Blackdiamond switches where you’ll find some real neat stuff going on. Expect to pay £8k upwards.

We’re about to get some new switches for testing our new storage platform – we’ll probably go for the Procurve 5406zl on this occasion. I’ll post more about that when we’ve made up our minds…

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