iSCSI SAN vs. fibre SAN?

I am planning to buy the hardware for a 2 server SQL cluster and I need some info about the SAN options.

I am looking at budget option: EMC Clarion AX150. If I buy the fiber version and 4 HBA's I'm looking at spending around £7k before any disks (I already have a couple of fiber switches with spare ports).

I'd like to know if I could save money by buying the iSCSI version without affecting performance too much.

My questions:

Will iSCSI have slower read/write speeds than fiber?

Do I need to buy iSCSI adapters for my servers or can I use the servers' on-board NIC's?

Can I use my existing Cisco rack switches for the iSCSI SAN?

Any help from you Wizards, Guru's and Masters would be appreciated. Thanks
clearchannelAsked:
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Duncan MeyersConnect With a Mentor Commented:
Will iSCSI have slower read/write speeds than fiber?
Yes, iSCSI is slower than FC, but the time taken and latency of the iSCSI or FC transaction is a relatively small compared to the overall speed of the discs.

Do I need to buy iSCSI adapters for my servers or can I use the servers' on-board NIC's?

That really depends on the applications you're running. I've seen figures that suggest that iSCSI HBA performance is approximately 70-80% compared to FC throughput, and loaded the CPU by an additional 5-10%. The MS iSCSI software initiator runs at approximately 50-60% of FC throughput and loads the CPU by 40%. Ouch. (Using iometer to generate load - 70% random, 30% sequential, 70% read, 30% write:)

Can I use my existing Cisco rack switches for the iSCSI SAN?
Yes. You need two subnets and two VLANs to separate the iSCSI traffic from the rest of your network, otherwise PowerPath multi-pathing won't work. Ideally, put the iSCSI traffic on its own switches.

A CX3-10C is the entry-level system for the CLARiiON range, and it's pretty economical. It supports fibre channel and iSCSI. Best of all, it expands up to 60 discs, unlike the AX150i which is a maximum of 12 discs.
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Hedley PhillipsOwnerCommented:
>> Will iSCSI have slower read/write speeds than fiber?

It is slower, but we don't notice any particular problems. I don't have the exact figures here but I am sure someone will post them.

>> Do I need to buy iSCSI adapters for my servers or can I use the servers' on-board NIC's?

You can use normal NIC's with Microsofts iSCSI software initiator running on top, this does create a slight overhead though.

>> Can I use my existing Cisco rack switches for the iSCSI SAN?

Any IP switch will work, obviosuly you want them as fast and stable as possible.


The good thing about iSCSI is the cost saving when it comes to the infrastrucure. We just have ours on Dell switches (use two for redundancy, Powerpath sorts out multiple pathing) and good Cat5.

Nice box the AX150i, solid and stable. The only issue with it is that it has a single backplane so this is the point of failure, but to have complete redundancy you would need to go up to the next level in Clarrion hardware and the prices really start to hurt.
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Duncan MeyersCommented:
I should mention: my preference is to use fibre channel if you can justify the additional cost, mostly for security. The storage network is then completely separate from your LAN, and there is less temptation for someone to "fix" or "improve" your iSCSI performance by mucking around with something they may not understand.
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clearchannelAuthor Commented:
Thanks to MeyersD and Mr Madcowz for the responses. I'll push for budget to get fiber but iSCSI looks like a good 2nd option.
Cheers
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