Geek Sync | Storage for the DBA

Editor's Notes

• #7: With block storage, files are split into evenly sized blocks of data, each with its own address but with no additional information (metadata) to provide more context for what that block of data is. You’re likely to encounter block storage in the majority of enterprise workloads; it has a wide variety of uses (as seen by the rise in popularity of SAN arrays). Object storage, by contrast, doesn’t split files up into raw blocks of data. Instead, entire clumps of data are stored in, yes, an object that contains the data, metadata, and the unique identifier. There is no limit on the type or amount of metadata, which makes object storage powerful and customizable. Metadata can include anything from the security classification of the file within the object to the importance of the application associated with the information. Anyone who’s stored a picture on Facebook or a song on Spotify has used object storage even if they don’t know it. In the enterprise data center, object storage is used for these same types of storage needs, where the data needs to be highly available and highly durable. However, object storage generally doesn’t provide you with the ability to incrementally edit one part of a file (as block storage does). Objects have to be manipulated as a whole unit, requiring the entire object to be accessed, updated, then re-written in their entirety. That can have performance implications. Another key difference is that block storage can be directly accessed by the operating system as a mounted drive volume, while object storage cannot do so without significant degradation to performance. The tradeoff here is that, unlike object storage, the storage management overhead of block storage (such as remapping volumes) is relatively nonexistent.
• #25: Compare the benefits and disadvantages of NVDIMM/Memory1 to NVMe.  NVMe or Non-Volatile Memory Express, sits on the PCIe bus (it’s not strictly a bus but a point-to-point connection).  PCIe is connected on the northbridge, so is closer to the processor.  Because it’s not a bus, PCIe doesn’t have the issues of a shared architecture and so can scale better.  Performance improves with each generation of PCIe and by aggregating channels or lanes together, a single device can deliver more throughput.  So flash devices that use NVMe can deliver high performance and low latency persistent storage.  Intel use NVMe for Optane drives, which have latencies as low as 10µs.  Standard flash-based NVMe drives can deliver performance in line with technologies like Memory1.  Don’t forget, many NVMe drives (in 2.5″ drive form factor) are also hot swappable.  It’s certainly not possible to hot-swap DIMMs.  NVMe flash drives also offer high capacity, compared to what was offered with Memory1. NVDIMM or non-volatile DIMM is a technology that uses the DRAM DIMM form factor and is directly plug compatible with system memory.  As the name suggests, the contents of the DIMM are not lost when the power is turned off.  Diablo calls this technology Memory Channel Storage, with the rest of the industry generally knowing as Storage Class Memory or SCM.  If we compare traditional (for example flash) storage to DRAM, one big difference is the way in which storage is addressed.  DRAM is byte-addressable, whereas flash is block-addressable.  Flash requires an entire block of data to be modified for an update – DRAM can do this at the byte level.