Solid-State Drives: Get One Already!
I've been building computers since the 1990s, so I've seen a lot of new technologies work their way into the mainstream. Most were the steady, incremental improvements predicted by Moore's law, but others were game-changers, innovations that really rocketed performance forward in a surprising way. I remember booting up Quake after installing my first 3-D card—what a difference! My first boot off a solid-state drive (SSD) brought back that same feeling—wow, what a difference!
However, at a recent gathering of like-minded Linux users, I learned that many of my peers hadn't actually made the move to SSDs yet. Within that group, the primary reluctance to try a SSD boiled down to three main concerns:
I'm worried about their reliability; I hear they wear out.
I'm not sure if they work well with Linux.
I'm not sure an SSD really would make much of a difference on my system.
Luckily, these three concerns are based either on misunderstandings, outdated data, exaggeration or are just not correct.
SSD Reliability Overview
How SSDs Differ from Hard Drives:
Traditional hard disk drives (HDDs) have two mechanical delays that can come into play when reading or writing files: pivoting the read/write head to be at the right radius and waiting until the platter rotates until the start of the file reaches the head (Figure 1). The time it takes for the drive to get in place to read a new file is called seek time. When you hear that unique hard drive chatter, that's the actuator arm moving around to access lots of different file locations. For example, my hard drive (a pretty typical 7,200 RPM consumer drive from 2011) has an average seek time of around 9ms.
Figure 1. Hard Drive
Instead of rotating platters and read/write heads, solid-state drives store data to an array of Flash memory chips. As a result, when a new file is requested, the SSD's internal memory can find and start accessing the correct storage memory locations in sub-milliseconds. Although reading from Flash isn't terribly fast by itself, SSDs can read from several different chips in parallel to boost performance. This parallelism and the near-instantaneous seek times make solid-state drives significantly faster than hard drives in most benchmarks. My SSD (a pretty typical unit from 2012) has a seek time of 0.1ms—quite an improvement!
Reliability and Longevity:
Reliability numbers comparing HDDs and SSDs are surprisingly hard to find. Fail rate comparisons either didn't have enough years of data, or were based on old first-generation SSDs that don't represent drives currently on the market. Though SSDs reap the benefits of not having any moving parts (especially beneficial for mobile devices like laptops), the conventional wisdom is that current SSD fail rates are close to HDDs. Even if they're a few percentage points higher or lower, considering that both drive types have a nonzero failure rate, you're going to need to have a backup solution in either case.
Apart from reliability, SSDs do have a unique longevity issue, as the NAND Flash cells in storage have a unique life expectancy limitation. The longevity of each cell depends on what type of cell it is. Currently, there are three types of NAND Flash cells:
SLC (Single Later Cell) NAND: one bit per cell, ~100k writes.
MLC (Multi-Layer Cell) NAND: two bits per cell, ~10k to 3k writes, slower than SLC. The range in writes depends on the physical size of the cell—smaller cells are cheaper to manufacture, but can handle fewer writes.
TLC (Three-Layer Cell) NAND: ~1k writes, slower than MLC.
Interestingly, all three types of cells are using the same transistor structure behind the scenes. Clever engineers have found a way to make that single Flash cell hold more information in MLC or TLC mode, however. At programming time, they can use a low, medium-low, medium-high or high voltage to represent four unique states (two bits) in one single cell. The downside is that as the cell is written several thousand times, the oxide insulator at the bottom of the floating gate starts to degrade, and the amount of voltage required for each state increases (Figure 2). For SLC it's not a huge deal because the gap between states is so big, but for MLC, there are four states instead of two, so the amount of room between each state's voltage is shortened. For TLC's three bits of information there are six states, so the distances between each voltage range is even shorter.
Figure 2. A NAND Flash Cell
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
Free to Linux Journal readers.Register Now!
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide