I've been a sysadmin for a long time, and part of being a sysadmin is doing more than is humanly possible. Sometimes that means writing wicked cool scripts, sometimes it means working late, and sometimes it means learning to say no. Unfortunately, it also sometimes means cutting corners. I confess, I've been "that guy" more than once. A good example is SELinux. On more than a few (hundred!) occasions, I've simply disabled SELinux, because getting things to work right is often really frustrating and time consuming. The same is true with LVM (Logical Volume Manager). I didn't get it. I thought it added an unnecessary layer of complexity. I thought it meant another potential point of failure. I thought it was stupid.
I was wrong.
LVM is an incredibly flexible, ridiculously useful and not terribly complicated to use system. It makes life easier. It makes future storage upgrades and migrations simple. Quite simply, I love it. So in this article, I cover the concepts and usage of LVM. By the time I'm done, hopefully you'll love it as much as I do!
What LVM Is
The best analogy I can come up with for explaining LVM is a SAN. If you've ever used a SAN (Storage Area Network) in your server environment, you know it abstracts the idea of individual hard drives and allows you to carve out "chunks" of space to use as drives. Rather than worrying about how big your hard drives might be, a SAN lets you throw all your hard drives into a big chassis and then allocate space to individual clients without being concerned about how many or how few physical drives are being used. LVM is sort of like that, but for an individual system rather than an entire network.
Figure 1 shows my poor attempt at drawing the concept of an LVM system. At first glance, it might seem like using an LVM is silly. Why combine a bunch of drives together, only to carve them up into virtual drives, right? Thankfully, that simple concept gives incredible flexibility down the road. Need a great big partition, but have only a bunch of smaller disks? No problem. Have only a couple disks now, but want to add more later without reformatting? No problem. Need to take snapshots, like with virtual servers, but you're using actual bare metal? No problem. LVM makes dealing with storage far better than partitioning drives or using a simple RAID setup (which, incidentally, brings me to the next issue).
Figure 1. It's important to think of my drawings as art—possibly second-grade art.
What LVM Isn't
With all the flexibility and expandability I mentioned in the previous paragraph, it seems like LVM would be a perfect replacement for hardware- or software-based RAID. After all, one of the big advantages of RAID is that multiple smaller drives can be used as a single, larger drive. For that particular feature, LVM is indeed ideal. Unfortunately, however, LVM doesn't provide any options for redundancy or parity. That means if you have a drive fail in LVM, you lose data. There's no such thing as striped LVM or mirrored LVM; it's simply not designed to do that.
LVM also isn't designed to increase speed by striping reads and writes across multiple disks. As block devices in the volume group fill up, such simultaneous read/writes may occur, but it's not by design and certainly not to gain speed. Hopefully, it's clear: LVM is really cool, but it is not in any way a replacement for RAID. Thankfully, it doesn't need to be.
(Note: recent versions of LVM actually do provide striping and mirroring features. In some cases, it can take the place of RAID completely. I still think understanding them as separate concepts is important. If you want to learn more about LVM and utilize the RAID features, I'll leave that as an exercise for you.)
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!
- SUSE LLC's SUSE Manager
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- My +1 Sword of Productivity
- Managing Linux Using Puppet
- Non-Linux FOSS: Caffeine!
- Doing for User Space What We Did for Kernel Space
- SuperTuxKart 0.9.2 Released
- Google's SwiftShader Released
- Parsing an RSS News Feed with a Bash Script
- Rogue Wave Software's Zend Server
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