Big data, it’s the buzz word of the year and it’s generating a lot of attention. An incalculable number of articles fervently repeat the words “variety, velocity and volume,” citing click streams, RFID tags, email, surveillance cameras, Twitter® feeds, Facebook® posts, Flickr® images, blog musings, YouTube® videos, cellular texting, healthcare monitoring …. (gasps for air). We have become a society that sweats buckets of data every day (the latest estimates are approximately 34GB per person every 24 hours) and businesses are scrambling to capture all this information to learn more about us.

Save every scrap of data!
“Save all your data” has become the new business mantra, because data – no matter how seemingly meaningless it appears – contains information, and information provides insight, and improved insight makes for better decision-making, and better decision-making leads to a more efficient and profitable business.

Okay, so we get why we save data, but if the electronic bit bucket costs become prohibitive, big data could turn into its own worst enemy, undermining the value of mining data.  While Hadoop® software is an excellent (and cost-free) tool for storing and analyzing data, most organizations use a multitude of applications in conjunction with Hadoop to create a system for data ingest, analytics, data cleansing and record management. Several Hadoop vendors (Cloudera, MapR, Hortonworks, Intel, IBM, Pivotal) offer bundled software packages that ease integration and installation of these applications.

Installing a Hadoop cluster to manage big data can be a chore
With the demand for data scientists growing, the challenge can become finding the right talent to help build and manage a big data infrastructure.  A case in point: Installing a Hadoop cluster involves more than just installing the Hadoop software. Here is the sequence of steps:

  1. Install the hardware, disks, cables.
  2. Install the operating system.
  3. Optimize the file system and operating system (OS) parameters (i.e. open file limits, virtual memory).
  4. Configure and optimize the network and switches.
  5. Plan node management (for Hadoop 1.x this would be Namenode, Secondary Namenode, JobTracker, ZooKeeper, etc.).
  6. Install Hadoop across all the nodes. Configure each node according to its planned role.
  7. Configure high availability (HA) (when required).
  8. Configure security (i.e. Kerberos, Secure Shell [ssh]).
  9. Apply optimizations (I have several years’ experience in Hadoop optimization, so can say with some authority that this is not a job to be taken lightly. The benefits of a well-optimized cluster are incredible, but it can be a challenge to balance the resources correctly without adding undo system pressure elsewhere.)
  10. Install and integrate additional software and connectors (i.e. to connect to data warehousing system, input streams or database management system [DBMS] servers).
  11. Test the system.

Setup, from bare bones to a simple 15-node cluster, can take weeks to months including planning, research, installation and integration. It’s no small job.

Appliances simplify Hadoop cluster deployments
Enter appliances: low-cost, pre-validated, easy-to-deploy “bricks.” According to a Gartner forecast (Forecast: Data Center Hardware Spending to Support Big Data Projects, Worldwide 2013), appliance spending for big data projects will grow from 0.9% of hardware spending in 2012 to 9.3% by 2017. I have found myself inside a swirl of new big data appliance projects all designed to provide highly integrated systems with easy support and fully tested integration. An appliance is a great turnkey solution for companies that can’t (or don’t wish to) employ a hardware and software installation team: Simply pick up the box from the shipping area, unpack it and start analyzing data within minutes. In addition, many companies are just beginning to dabble in Hadoop, and appliances can be an easy, cost-effective way to demonstrate the value of Hadoop before making a larger investment.

While Hadoop is commonplace in the big data infrastructure, the use models can be quite varied. I’ve heard my fair share of highly connected big data engineers attempt to identify core categories for Hadoop deployments, and they generally fall into one of four categories:

  1. Business intelligence, querying, reporting, searching – such as filtering, indexing, trend analysis, search optimization – and good old-fashioned information retrieval.
  2. Higher performance for common data management operations including log storage, data storage and archiving, extraction/transform loading (ETL) processing and data conversions.
  3. Non database applications such as image processing, data sequencing, web crawling and workflow processing.
  4. Data mining and analytical applications including social network/sentiment analysis, profile matching, machine learning, personalization and recommendation analysis, ad optimization and behavioral analysis.

Finding the right appliance for you
While appliances lower the barrier to entry to Hadoop clusters, their designs and costs are as varied as their use cases.  Some appliances build in the flexibility of cloud services, while others focus on integration of applications components and reducing service level agreements (SLAs). Still others focus primarily on low cost storage. And while some appliances are just hardware (although they are validated designs), they still require a separate software agreement and installation via a third-party vendor.

In general, pricing is usually quoted either by capacity ($/TB), or per node or rack depending on the vendor and product. Licensing can significantly increase overall costs, with annual maintenance costs (software subscription and support) and license renewals adding to the cost of doing business. The good news is that, with so many appliances to choose from, any organization can find one that enables it to design a cluster that fits its budget, operating costs and value expectations.

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Customer dilemma: I just purchased PCIe® flash cards to increase performance of my enterprise applications that run on Linux® and Unix®. How do I set them up to get the best performance?

Good question. I wish there were a simple answer but each environment is different. There is no cookie-cutter configuration that fits all, though a few questions will reveal how the PCIe flash cards should be configured for optimum performance.

Most of the popular relational and non-relational databases run on many different operating systems. I will be describing Linux-specific configurations, but most of them should also work with Unix systems that are supported by the PCIe flash card vendor. I’m a database guy, but these same principals and techniques that I’ll be covering apply to other applications like mail servers, web servers, application servers and, of course, databases.

Aligning PCIe flash devices
The most important step to perform on each PCIe flash card is to create a partition that is aligned on a specific boundary (such as 4k or 8k) so each read and write to the flash device will require only one physical input/output (IO) operation. If the card is not partitioned on such a boundary, then reads and writes will span the sector groups, which doubles the IO latency for each read or write request.

To align a partition, I use the sfdisk command to start a partition on a 1M boundary (sector 2048). Aligning to a 1M boundary resolves the dependency to align to a 4k, 8k, or even a 64k boundary. But before I do this, I need to know how I am going to use this device. Will this be a standalone partition? Part of a logical volume? Or part of a RAID group?

Which one is best?
If I were deploying the PCIe flash device for database caching (for example, the Oracle database has provided this caching functionality for years using the Database Smart Flash Cache feature, and Facebook created the open source Flashcache used in MySQL databases), I would use a single-partitioned PCIe flash card if I knew the capacity would meet my needs now and over the next 5 years. If I selected this configuration, the sfdisk command to create the partition would be:

echo “2048,,” | sfdisk –uS /dev/sdX –force

This single partitioning is also required with the Oracle® Automatic Storage Management system (ASM). Oracle has provided ASM for many years and I will go over how to use this storage feature in Part 3 of this series.

If I need to deploy multiple PCIe flash cards for database caching, I would create Logical Volume Manager (LVM) over all the flash devices to simplify administration. The sfdisk command to create a partition for each PCIe flash card would be:

echo “2048,,8e” | sfdisk –uS /dev/sdX –force

“8e” is the system partition type for creating a logical volume.

Neither of these solutions needs fault tolerance since they will be used for write-thru caching. My recent blog “How to optimize PCIe flash cards – a new approach to creating logical volumes” covers this process in detail.

If I want to use the PCIe flash card for persisting data, I would need to make the PCIe flash cards fault tolerant, using two or more cards to build the RAID array and eliminate any single point of failure. There are a number of ways to create a RAID over multiple PCIe flash cards, two of which are:

  • Use LVM with the RAID option.
  • Use the software RAID utility MDADM (multiple device administration) to create the RAID array.

But what type of RAID setup is best to use?
Oracle coined the term S.A.M.E. – Stripe And Mirror Everything – in 1999 and popularized the practice, which many database administrators (DBA) and storage administrators have followed ever since. I follow this practice and suggest you do the same.

First, you need to determine how these cards will be accessed:

  • Small random reads and writes
  • Larger sequential reads
  • Hybrid (mix of both)

In database deployments, your choice is usually among online transaction processing (OLTP) applications like airline and hotel reservation systems and corporate financial or enterprise resource planning (ERP) applications, or data warehouse/data mining/data analytics applications, or a mix of both environments. OLTP applications involve small random reads and writes as well as many sequential writes for log files. Data warehouse/data mining/data analytics applications involve mostly large sequential reads with very few sequential log writes.

Before setting up one or many PCIe flash cards in a RAID array either using LVM on RAID or creating a RAID array using MDADM, you need to know the access pattern of the IO, capacity requirements and budget. These requirements will dictate which RAID level will work best for your environment and fit your budget.

I would pick either a RAID 1/RAID 10 configuration (mirroring without striping, or striping and mirroring respectively), or RAID 5 (striping with parity). RAID 1/RAID 10 costs more but delivers the best performance, whereas RAID 5 costs less but imposes a significant write penalty.

Optimizing OLTP application performance
To optimize performance of an OLTP application, I would implement either a RAID 1 or RAID 10 array. If I were budget constrained, or implementing a data warehouse application, I would use a RAID 5 array. Normally a RAID 5 array will produce a higher throughput (megabits per second) appropriate for a data warehouse/data mining application.

In a nutshell, knowing how to tune the configuration to the application is key to reaping the best performance.

For either RAID array, you need to create an aligned partition using sfdisk:

echo “2048,,fd” | sfdisk –uS /dev/sdX –force

“fd” is the system identifier for a Linux RAID auto device.

Keep in mind that it is not mandatory to create a partition for LVMs or RAID arrays. Instead, you can assign RAW devices. It’s important to remember to align the sectors if combining RAW and partitioned devices or just creating a basic partition. It’s sound practice to always create an aligned partition when using PCIe flash cards.

At this point, aligned partitions have been created and are now ready to be used in LVMs or RAID arrays. Instructions for creating these are on the web or in Linux/Unix reference manuals. Here are a couple of websites that go over the process of creating LVM, RAID, or LVM on RAID:

https://raid.wiki.kernel.org/index.php/Partitioning_RAID_/_LVM_on_RAID
http://www.gagme.com/greg/linux/raid-lvm.php

Specifying a stripe width value
Also remember that, when creating LVMs with striping or RAID arrays, you’ll need to specify a stripe width value. Many years ago, Oracle and EMC conducted a number studies on this and concluded that a 1M stripe width performed the best as long as the database IO request was equal to or less than 1M. When implementing Oracle ASM, Oracle’s standard is to use 1M allocation units, which matches its coarse striping size of 1M.

Part 2 of this series will describe how to create RAW devices or file systems.

Part 3 of this series will describe how to use Oracle ASM when deploying PCIe flash cards.

Part 4 of this series will describe how to persist assignment to dynamically changing NWD/NMR devices.

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