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So Which Is Better?
As with many things in computing, "It depends on many factors, issues, and requirements." About a year and a half ago, my company was asked to work on a project where the customer wanted to use enterprise storage for capturing high-speed data streams. Internally, we called this project BFASP -- "blood from a stone project." We knew, as did many of the other technical people involved, that the customer could not use an enterprise storage box for high-speed, full duplex I/O (writing files and reading other files at the same time).
The enterprise storage vendors benchmark team said they could do this type of I/O, but our technical team thought this was absurd. After spending 36 hours with them, the benchmark team finally came to this conclusion: "Oh, we did not understand you needed full duplex I/O at these speeds; we cannot do this." The customer ended up purchasing a storage-centric RAID, and the enterprise storage vendor left with their tails between their legs, as they should have, given the time and money that was wasted.
On the other hand, the same enterprise storage box will far exceed the performance of the storage-centric device for a database where the index files are used often and fit into the cache. A few new vendors are entering the market and claiming to combine the best of both products. Vendors such as EMC with its new DMX2000, 3ParData, and others will be seeking to prove their products can ably perform both functions.
The decision on what to buy is quite often far above your pay grade, but assuming that you do have some say, or at least have some input, you need to review your requirements and your operational usage. Here are just a few of the major issues that you should consider:
- What are the uptime and reliability requirements?
- What are your backup requirements?
- What RAID level will you be using?
- How large are your files typically, and how are they accessed?
It comes down to how much downtime you can afford for the box. If you have many attached hosts, you cannot afford any downtime. This is often called the 9 count, or how many "9s" of reliability are supported. Here's a chart showing several different combinations of "9s" and their corresponding downtime:
Downtime Per Year in Seconds
Downtime in Minutes Per Year
Downtime in Hours Per Year
Downtime in Days Per Year
Knowing the reliability requirements and the number of attached hosts will help determine the type of equipment needed.