I’ve noticed a few blog posts recently about speed of deduplication in the modern data center. I agree that speed is an important factor, but keep in mind that not all dedupe is created equal. That is to say, fast is good, but only if you are also effective. One of the tricky things has been that the easiest data to compress is also usually the most carefully performance tuned. A great example of this is a database. This is because databases are comprised of simple alphanumeric fields and sparse tables. All of that is easy to reduce in size.
However, a company’s core transactional database is the most conservative asset in the data center. Introducing compression would save space, for sure, but you could only use very fast, simple compressors there. At the same time, customers will be hesitant to deploy a new layer of processing in their most sensitive application.
So, where is most data growth? In fact, it’s being driven by unstructured data – Office documents, rich media, email with attachments, PDFs, Flash videos, and so forth. This complex data does not lend itself to fast simple compressors. But perhaps we should back up for a moment and think about how customers have been behaving all along.
Throughout the history of storage, there have always been tradeoffs available between fast expensive storage, and slower but cheaper alternatives. This is not a bad thing. It gives users alternatives based on their priorities and budgets. Back in the old mainframe days, these choices were between very expensive mainframe memory and “offline” storage like drums, cards, and tapes. Today the technology is all much bigger, faster, cheaper and sexier. But really, the tradeoffs are the same.
Data reduction technology adds another layer of choice above and beyond the traditional hardware choices. Now in addition to choosing whether you want fast, expensive solid state disk (SSD) or slower but very cost-effective SATA, you can also choose whether you want to compress and/or deduplicate the data that is stored on those disks.
Just like physical disks, compression and dedupe come in a range of speeds and capabilities. There are simple and very fast compressors that are essentially invisible in terms of their impact on storage performance. There are more complex compressors that get better results, but which may take longer, either to compress or to decompress the data. Deduplication, done well, should always be pretty fast, and streaming dedupe rates of well of 300MB/sec are now available from many vendors (including Data Domain and Ocarina).
The emergence of tools to automatically tier data to its appropriate place help make the use of all of these technologies more feasible. That applies as much to solid state disks as it does to dedupe and compression. When data tiering can be made invisible to end-users and applications, then implementing multiple physical and logical tiers of storage becomes practical. Good examples would include EMC’s new FAST tools, Compellent’s “Fluid Data Storage”, and HDS’s Data Migrator. When users or administrators have to move data by hand to get it to a compressed tier or a solid state disk, then the operational costs offset the capital savings.
You might want to be wary when someone’s biggest claim to fame is fast dedupe. Just as the old mainframe admin had to decide whether something was important enough to live in RAM, or could be stored on cheaper tapes instead, today’s IT shops have to decide where it is most important to try to get data reduction, and what tool will get the most bang for the buck for that kind of data. You need the whole story, and then you can decide based on your own priorities.
