Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

We have a couple servers hosting Citrix VM's. We are planning on adding SAN storage to our network so that we can do the quick migration and high availability thing. The question comes up with deciding what NICs to buy for the servers. We have scads of available pci(e) slots on the servers, so density is not a factor. We're not going to do 10Gbs.

The concerns are gigabit, jumbo frame support (which any old nic is apparently capable of) and making sure none of the processing load is put on the server itself (no softmodem type deal).

I see some nics advertise "copper connection." Is there any benefit to that? What other options should I not compromise on?

Wouldn't it be preferred to have single port nics over dual for redundancy purposes? That's kinda what I gathered from this SF thread.

The San setup we're looking at if anyone's interested:

Clariion: http://www.emc.com/collateral/hardware/data-sheet/h4097-clariion-ax4-ds.pdf (data sheet) http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=6076470 $9679.99

OR

Dell: http://www.dell.com/us/business/p/powervault-md3200i/pd?refid=powervault-md3200i&baynote_bnrank=0&baynote_irrank=1&~ck=dellSearch $10,749 (not configured as printed--baseline 1tb) $12,905.00 (8tb configured)

Managed Switch: http://www.newegg.com/Product/Product.aspx?Item=N82E16833122074 x1 $599 OR http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3334993&sku=C50-2162 x1 $350

Edit: to clarify the intent of the SAN setup, the illustration below shows the added isolated network we are adding on for the storage for the 2 xen servers. We don't (I believe) need a fancy switch, just one with jumbo frame capability, standard management features and vlan capability: alt text

share|improve this question
2  
Just to be clear, on that other thread you link to, I suggested a cheap desktop NICs because he had an older server acting as a firewall for s smallish link. IMO, the answer to that question is completely unrelated to your question. Virtual machines and SANs need a much better infrastructure. –  Zoredache Dec 15 '10 at 19:03
    
So if I used this Dell dell.com/us/business/p/powerconnect-5424/pd and VLAN, would that negate any advantage of isolating this proposed addition from the current network? Is this: accessories.us.dell.com/sna/… a respectable NIC for this setup? –  Detritus Maximus Dec 15 '10 at 23:01
add comment

3 Answers 3

up vote 4 down vote accepted

You're asking about doing a small iSCSI SAN, and you're on the right track. We do something very similar with Dell servers and MD3000i arrays.

In the diagram provided, you show two links from server to switch. I think you can get away with one link, unless you're bonding them for greater throughput. As shown, the arrangement protects against failure of the server NIC, the cable, and the port on the switch. A better (high-dollar) approach would be to add a second switch, and connect each Server to each switch, and cross connect the switches. That protects against loss of an entire switch, but adds the complexity of Spanning Tree, which is the Layer2 protocol for preventing the loop that otherwise appears in the network when 2 switches are introduced. From there, the two switches are commonly attached to two SAN heads, which themselves are cross-connected.. but that's larger scale than you've asked about. Go single-path the whole way, and accept the marginal increased risk in trade for ease of care & feeding.

Regarding ease of care & feeding: Think long and hard about the relative likelihood of hardware failure versus wetware failure. I feel like I see 5:1 ratio of human goofs versus actual HW fail, and so if you're not going to do the mega-buck fully-redundant-everything, keep it simple.

If you enable Jumbo Frames, you've got to do Jumbo Frames everywhere on that network. You've sketched out a dedicated storage network, so you can do it - I'm not so fortunate.

If you ARE bonding those server NICs for throughput, consider adding more bonded interfaces from the switch to the SAN head. If each of N servers is doing X traffic, the san needs to keep up with NX traffic, minus some small oversubscription fudge factor.

I believe the "copper connection" you've asked about is simply copper CAT6 twisted-pair ethernet, as used for iSCSI. As you move into the higher-end SAN world, you see more optical fiber connections, and HBA cards with various modular physical connectors - SFP, GBIC, etc.

Tangentially, how are you dividing up user sessions between the Citrix servers? Is there any sort of active loadbalancing in place (Netscaler?) If you have HA Xen servers, how does the failover process look from the user perspective? Make sure you've identified the mechanism by which this SAN actually improves things for the users.

Edited to add: You might also price out a more traditional shared direct-attach storage cluster. I do these with Windows, so I don't have the details around Xen/Linux, but it's a SAS disk shared between the two nodes. Example being the Dell MD3000 (not the "i" model). (With Dell, you need the proper HBA too, SAS 5/e, iirc) If you're never going to add more compute nodes, the SAS cluster might be easier & cheaper to build. Whatever you end up doing: Validate & Test, test, test. In my experience folks build a cluster to add "high availability" without defining what that means in real terms, and then don't validate that it protects them against the failures they were expecting (hoping, really) against.

share|improve this answer
1  
You mention bonding several times, but it usually it isn't very helpful in connections to an iSCSI SAN since you will usually only have a small number of connections open. Typical bonding policies will force a single connection to be tied to a single interface from the group of bonded interfaces. Bonding may be able to help with some switches, and some configurations, but it will almost never be helpful on a cheap low-end switch. –  Zoredache Dec 15 '10 at 19:35
    
That's why I mentioned cross-stack LACP and a second switch. –  pfo Dec 15 '10 at 19:46
    
The HA automatically brings back critical VMs that drop out of the pool due to hardware failure on one of the servers. We have a few VMs that are critical that we will designate for this feature. In order to have HA, we must have iSCSI or FC storage repository--see support.citrix.com/article/CTX119717--the pdf/whitepaper. If nobody's around and one of the 2 crashes, the other will bring up designated VMs. Do you think this could be done with the MD3000? –  Detritus Maximus Dec 15 '10 at 22:39
    
Per the first paragraph on page 2 of the HA guide, it sounds like the direct attach MD3K is not workable. Xen really wants to use FC or iSCSI to do the heartbeat - The storage drivers are using reservations or somesuch, and while modern MPIO SAS drivers probably do support those semantic features, you'd be bending and or battling Xen the whole way... not worth it. Go iSCSI. –  AndyN Dec 15 '10 at 22:54
    
Since nobody has mentioned it yet: Buy a NIC that's on the Xen Hardware Compatibility List: hcl.vmd.citrix.com/BrowsableNICList.aspx –  AndyN Dec 16 '10 at 1:20
add comment

Wait - you're asking for server grade NICs but want to buy a 350 bucks switch?! I don't get that ...

Usually "server grade" 48 port GigE switches go for somewhere around 3000-5000 USD list price. Maybe you want to look out for switch side things like stacking for cross-stack LACP.

Regarding the NIC, things like:

  • proper DMA interface and good drivers that support MSI-X interrupts (check reviews on performance for that)
  • matching PCI-E interface speed
  • multiple ports if needed
  • TCP offload engine
  • L2 features like 802.1Q and 802.1X
  • iSCSI offload engine
  • GBIC support if you need to mix and match WAN and LAN on same NIC
share|improve this answer
    
What in the world do I need 48 ports for? I just need a dedicated path between my SAN and the 2 servers? I could do it with an 8 port managed switch. Maybe I need to edit my post and explain that part... –  Detritus Maximus Dec 15 '10 at 16:18
    
Well the 24 port versions are roughly half in price. –  pfo Dec 15 '10 at 16:24
3  
You mean, two lines to each of the two servers and two lines to the SAN? Come on, this isn't a text message. –  DanBig Dec 15 '10 at 16:35
4  
OP's question kinda reduces to "What are the cheapest tires I can put on my Ferrari?" A business case that really calls for a SAN pre-supposes server-class hardware. Unless you're doing it for training/practice, in which case, buying a new Clariion sounds like madness. Finally, if you are going to roll your own, know that many of the fancy SAN features like snapshotting and replication are licensed software, and may cost more than the hardware you're proposing. –  AndyN Dec 15 '10 at 17:43
2  
Designing new systems is about balance of components and the right choice of equipment. Especially when it comes to your storage and it's network you should have an eye on well chosen equipment that is bullet proof and performs well. A lowest end linksys consumer switch doesn't fit to an EMC array. –  pfo Dec 15 '10 at 18:09
show 5 more comments

So what really makes a server grade NIC?

Primarily quality.

From a manufacturing point the differences between a server and "consumer" grade NIC are somewhat similar to the differences between a proper server motherboard and the one in an ordinary PC. First, the components are generally higher grade, selected with tighter tolerances and higher reserve margins. There will also normally be better protection circuitry to protect against damaged caused by out of tolerance voltages, such as spikes induced in a network cable that might fry a regular NIC.

The chipsets used will generally have some level of redundancy, where parts of the circuit can be switched in and out as required to handle fault conditions. Not at all unlike having redundant power supplies in the server.

The firmware is also likely to be better in a server grade NIC, which usually allows it to handle network conditions that might bring a regular NIC to its proverbial knees.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.