Tuesday, September 2, 2008

iSCSI - SAN for Small (and big players)

For years all the buzz in storage has centered around 3 letters SAN. The storage area network, fast, centralized, flexible, resilient. Placing storage directly in each server is costly, inefficient, risky, and slow. And for some number of years vendors and partners and such 'hid' this term from smaller shops due to costs involved with a SAN architecture that was designed to meet all the marketing accolades. Fibre channel equipment was really the only option.

A new technology began to surface 3-4 years ago - i(nternet)SCSI. I won't rehash all the details that Wikipedia can provide except for the main point of iSCSI - commodity interconnects. iSCSI allows for the use of common networking equipment: switches, NICs, cables. iSCSI does not require the use of $1K+ HBA's, fragile cabling and specialized directors/switches, etc. The reality of iSCSI's pratical use is here due to the commoditization of gigabit ethernet and soon to be 10gig ethernet.

iSCSI also brought options to storage subsystems. No longer are costly FC drives the only option, but also SCSI, SAS, and even SATA. A multi terabyte array can be obtained or even constructed for costs well within reach of nearly any business. iSCSI can also (and often does) exist a strictly software world - no HBA'$ required. Some argue the software overhead is detrimental to overall system performance. I'd argue today's systems have sufficient processing capacity to run software iSCSI in situations where iSCSI is a good fit.

With this commoditization of the SAN, vendors have been quick to offer up 'solutions' for smaller shops. I have a caution to throw out that requires a little lesson on storage. First off, the most important item in selecting the proper storage is understanding the application(s) that will access it. I can't elaborate on this enough - don't even start to think about how much space you'll need until the application is understood. In fact refuse to talk about capacity with any vendor until this is ironed out. Try throwing a few virtual machines at solution that only does (or has been configured for) RAID 5, along with a file server, or mail server - it will not make you feel good about the money spent. At one point I had a prominent vendor's rep suggest a 4 spindle SATA system to me to replace a (6) disk file server and an Exchange server. All that person was concerned about was how much space and quoting his cheapest offering to improve the chance of a sale. I don't carry any certification badges, but I am well informed and experienced, and I know when I'm getting a snow job.

I ended up with a 16 SATA drive over two 3ware controllers system running linux and the open source iSCSI Enterprise Target software to provide my iSCSI storage. It's been rock solid. Its 8 drive RAID10 ran up against performance issues after a handful of VM's where thrown on it, but in all fairness virtualization was not in the picture when the system was spec'd. The next iteration will be 15K SAS based for VM storage.

So why use a SAN/iSCSI? A few main concepts are modularization and maximizing the storage investment. By detaching storage from a specific system several benefits are realized: 1) Smaller form factor systems can be purchased since they don't need to be filled with drives. 2) In the event of a system failure the storage can be accessed by a different system. 3) It fits into a virutalization environment for lots of reasons. 4) Designed right it will be faster than local storage. 5) Because multiple systems utilize space on the iSCSI server, the disk investment-to-utilization ratio is typically better.

Downsides include: 1) Slightly complicates overall architecture, 2) Small bit of iSCSI management expertise, 3) Many eggs in one basket situation(get a good warranty). With the right system and financial resources the iSCSI server can be setup to mirror with another system for improved reliability.

Know your applications, read about technology and reviews, search vendor support forums/blogs for real world feedback on your purchasing considerations.

Storage Advisors Have LOTS of great blogs on RAID levels/storage and their INs & OUTs


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Matt said...


Anonymous said...

I like iSCSI for exactly what you said...easy to access from multiple machines.. I use an ATTO iPBridge to connect to some of my older SCSI Drives and it allows you to see them on your iSCSI SAN.. they had a fibre channel version too... there are so many cool products out there today for networking that don't cost an arm and a leg and can really help your workflow!

JeffHengesbach said...

iceedge99 - Thanks, that's a really interesting looking product from ATTO!