iSCSI Best Practices

If you have stumbled on this page it because you are looking to implement iSCSI, maybe you’re new to this or maybe you’re a seasoned expert refreshing on the best practices around iSCSI.

For Pure Storage – Best Practices Link:  https://support.purestorage.com/Solutions/SAN/Best_Practices/SAN_Guidelines_for_Maximizing_Pure_Performance

Here are some key takeaways from the link.

• Do not route iSCSI
• VLAN Tagging is supported
• Use more interfaces with iSCSI
• Verify paths are clean
• MTU Speeds – use jumbo frames: 9000

Now, you probably asking yourself if how many ports do you need. This is a great questions and it high depends on your array, network, application, traffic, bandwidth, and more.

To understand how many ports I need and what port speed should I use, let’s first understand how to breakdown network bandwidth.

• 1 Gbps = 125 MBps = 0.125 GBps
• 10 Gbps = 1250 MBps = 1.25 GBps
• 25 Gbps = 3125 MBps = 3.125 GBps
• 40 Gbps = 5000 MBps = 5 GBps
• 100 Gbps = 12500 MBps = 12.5 GBps

Let’s look at sizing, for a FlashArray we size based on a number of inputs, we do NOT want to give you hero numbers, we want to size for real world workloads. Check out my sizing post here.

Let’s assume we are going to get (75% Read) (25% Write) 64K IO, or about 7340MBps (or 127.74K IOPS) out of an array. We want to target our port usage to around 7.5GBps (or 7340MBps)

In the above scenario if we choose network port speed at 100Gb, we use less ports, but is that a good thing? (remember best practice states more ports is better)

Summary –

• Use as many ports has you can, 8 paths with iSCSI is ideal.
• Understand your workloads so that we can size the arrays accordingly.
• Workload, peak vs sustained would determine if you need faster network or more network.
• Use VLANs to eliminate noisy neighbors
• There is no magic formula, but the above information can help size and define your ports
• Spend some time and read the link above.