SSD, flash and DRAM, DejaVu or something new?

Recently I was in Europe for a couple of weeks including stops at Storage Networking World (SNW) Europe in Frankfurt, StorageExpo Holland, Ceph Day in Amsterdam (object and cloud storage), and Nijkerk where I delivered two separate 2 day, and a single 1 day seminar.

At the recent StorageExpo Holland event in Utrecht, I gave a couple of presentations, one on cloud, virtualization and storage networking trends, the other taking a deeper look at Solid State Devices (SSD’s). As in the past, StorageExpo Holland was great in a fantastic venue, with many large exhibits and great attendance which I heard was over 6,000 people over two days (excluding exhibitor vendors, vars, analysts, press and bloggers) which was several times larger than what was seen in Frankfurt at the SNW event.

Both presentations were very well attended and included lively interactive discussion during and after the sessions. The theme of my second talk was SSD, the question is not if, rather what to use where, how and when which brings us up to this post.

For those who have been around or using SSD for more than a decade outside of cell phones, camera, SD cards or USB thumb drives, that probably means DRAM based with some form of data persistency mechanisms. More recently mention SSD and that implies nand flash-based, either MLC or eMLC or SLC or perhaps emerging mram or PCM. Some might even think of NVRAM or other forms of SSD including emerging mram or mem-resistors among others, however lets stick to nand flash and dram for now.

Often in technology what is old can be new, what is new can be seen as old, if you have seen, experienced or done something before you will have a sense of DejaVu and it might be evolutionary. On the other hand, if you have not seen, heard, experienced, or found a new audience, then it can be revolutionary or maybe even an industry first ;).

Technology evolves, gets improved on, matures, and can often go in cycles of adoption, deployment, refinement, retirement, and so forth. SSD in general has been an on again, off again type cycle technology for the past several decades except for the past six to seven years. Normally there is an up cycle tied to different events, servers not being fast enough or affordable so use SSD to help address performance woes, or drives and storage systems not being fast enough and so forth.

Btw, for those of you who think that the current SSD focused technology (nand flash) is new, it is in fact 25 years old and still evolving and far from reaching its full potential in terms of customer deployment opportunities.

Nand flash memory has helped keep SSD practical for the past several years riding the similar curve that is keeping hard disk drives (HDD’s) that they were supposed to replace alive. That is improved reliability, endurance or duty cycle, better annual failure rate (AFR), larger space capacity, lower cost, and enhanced interfaces, packaging, power and functionality.

DRAM historically at least for enterprise has been the main option for SSD based solutions using some form of data persistency. Data persistency options include battery backup combined with internal HDD’s to de stage information from the DRAM before power was lost. TMS (recently bought by IBM) was one of the early SSD vendors from the DRAM era that made the transition to flash including being one of the first many years ago to combine DRAM as a cache layer over nand flash as a persistency or de-stage layer. This would be an example of if you were not familiar with TMS back then and their capacities, you might think or believe that some more recent introductions are new and revolutionary, and perhaps they are in their own right or with enough caveats and qualifiers.

An emerging trend, which for some will be Dejavu, is that of using more DRAM in combination with nand flash SSD.

Oracle is one example of a vendor who IMHO rather quietly (intentionally or accidentally) has done this in the 7000 series storage systems as well as ExaData based database storage systems. Rest assured they are not alone and in fact many of the legacy large storage vendors have also piled up large amounts of DRAM based cache in their storage systems. For example EMC with 2TByte of DRAM cache in their VMAX 40K, or similar systems from Fujitsu HP, HDS, IBM and NetApp (including recent acquisition of DRAM based CacheIQ) among others. This has also prompted the question of if SSD has been successful in traditional storage arrays, systems or appliances as some would have you believe not, click here to learn more and cast your vote.

So is the future in the past? Some would say no, some will say yes, however IMHO there are lessons to learn and leverage from the past while looking and moving forward.

Early SSD’s were essentially RAM disks, that is a portion of main random access memory (RAM) or what we now call DRAM set aside as a non persistent (unless battery backed up) cache or device. Using a device driver, applications could use the RAM disk as though it were a normal storage system. Different vendors springing up with drivers for various platforms and disappeared as their need were reduced with faster storage systems, interfaces and ram disks drives supplied by vendors, not to mention SSD devices.

Oh, for you tech trivia types, there was also database machines from the late 80’s such as Briton Lee that would offload your database processing functions to a specialized appliance. Sound like Oracle ExaData I, II or III to anybody?

Ok, so we have seen this movie before, no worries, old movies or shows get remade, and unless you are nostalgic or cling to the past, sure some of the remakes are duds, however many can be quite good.

Same goes with the remake of some of what we are seeing now. Sure there is a generation that does not know nor care about the past, its full speed ahead and leverage what will get them there.

Thus we are seeing in memory databases again, some of you may remember the original series (pick your generation, platform, tool and technology) with each variation getting better. With 64 bit processor, 128 bit and beyond file system and addressing, not to mention ability for more DRAM to be accessed directly, or via memory address extension, combined with memory data footprint reduction or compression, there is more space to put things (e.g. no such thing as a data or information recession).

Lets also keep in mind that the best IO is the IO that you do not have to do, and that SSD which is an extension of the memory map plays by the same rules of real estate. That is location matters.

Thus, here we go again for some of you (DejaVu), while for others get ready for a new and exciting ride (new and revolutionary). We are back to the future with in memory database which while for a time will take some pressure from underlying IO systems until they once again out grow server memory addressing limits (or IT budgets).

However for those who do not fall into a false sense of security, no fear, as there is no such thing as a data or information recession. Sure as the sun rises in the east and sets in the west, sooner or later those IO’s that were or are being kept in memory will need to be de-staged to persistent storage, either nand flash SSD, HDD or somewhere down the road PCM, mram and more.

There is another trend that with more IOs being cached, reads are moving to where they should resolve which is closer to the application or via higher up in the memory and IO pyramid or hierarchy (shown above).

Thus, we could see a shift over time to more writes and ugly IOs being sent down to the storage systems. Keep in mind that any cache historically provides temporal relieve, question is how long of a temporal relief or until the next new and revolutionary or DejaVu technology shows up.

Ok, go have fun now, nuff said.

Cheers gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press, 2011), The Green and Virtual Data Center (CRC Press, 2009), and Resilient Storage Networks (Elsevier, 2004)

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