IBM's Journaled Filesystem
In the previous section, we explained how to create a JFS filesystem using an existing spare partition. Now, we demonstrate how to migrate your current system from another filesystem, such as ext2, to JFS. We look at how to introduce a JFS partition to your Linux configuration. In a second step, we make that partition the root filesystem.
What partition scheme do you need to create a JFS root partition? The migration process requires an empty partition. Let's assume that /dev/hda5 is the current root partition and that it uses ext2. We use /dev/hda6, which is our empty partition, as our JFS root partition. This partition needs to be of equal or larger size than the current root partition. The ext2 partition will be duplicated on the JFS partition. Afterward, if you do not wish to keep the ext2 partition, you can reformat it without losing your Linux system.
In order to create a root JFS partition on /dev/hda6, follow the instructions mentioned earlier to get support for JFS in the kernel. To make this partition a bootable partition for Linux, you need to reproduce a complete Linux installation. A simple way of doing so is to copy all the files to the JFS partition. First, mount the filesystem:
% mount -t jfs /dev/hda6 /jfs
Then, copy all files from ext2 filesystem to the JFS partition:
% cd / % cp -a bin etc lib boot dev home usr var [...] /jfs You need special handling for /proc and /tmp: % mkdir /jfs/proc % chmod 555 /jfs/proc % mkdir /jfs/tmp % chmod 1777 /jfs/tmpIt is important to create /proc and /tmp with the correct permissions. Permission 1777 means the only people who can rename or remove any file in that directory are the file's owner, the directory's owner and the superuser. The last steps involve changing /etc/lilo.conf and /etc/fstab. First, we change lilo.conf to boot using the kernel on our JFS partition. Notice that root is different from the first entry we made as well as from the label. Thus, the image to be booted will not be found in /dev/hda5/boot, but in /dev/hda6/boot:
image=/boot/vmlinuz-jfs label=jfs-kernel read-only root=/dev/hda6Finally, we need to change /jfs/etc/fstab to tell the Linux system what filesystem it is using. Change the following line:
LABEL=/ / ext2 defaults 1 1so that it says:
/dev/hda6 / jfs defaults 1 1Now, you can reboot and choose jfs-kernel. This will start Linux with the JFS root filesystem.
After a crash, the log replay occurs automatically. Instead of the usual fsck messages, you should see JFS journaling messages. Replaying the log is necessary when a filesystem becomes unstable.
One of the responsibilities of the Open Systems Lab at Ericsson Research is to design, implement and benchmark carrier-class platforms that run telecom applications. These carrier-class platforms have strict requirements regarding scalability, reliability and high availability. They must operate nonstop, regardless of hardware or software errors, and they must allow operators to upgrade hardware and software during operation without disturbing the applications that run on them. As a result, they must offer extreme reliability and high availability, often referred to as a five-nines availability (99.999% uptime).
To maintain such availability, these carrier-class platforms were designed with many features that allow software to be upgraded while the system is running and providing service. These features include fault tolerance implemented in the software, network redundancy to handle catastrophic situations such as earthquakes and in-service upgrade features.
Although many precautions have been taken to protect the system, there is always a remote chance that the processor (or server node) will fail. Thus, as a last resort, we need to reboot the processor. In this extreme case, we need to be able to reboot the processor and bring it to normal status, serving requests as soon as possible, with a minimal downtime.
Our interest in journaling filesystems for the carrier-class Linux platform came from the fact that these filesystems provide a fast filesystem restart. In the case of a system crash, a journaling filesystem can restore a filesystem to a consistent state more quickly and more reliably than other filesystems.
Initially, we started to experiment with the IBM JFS in early 2000. The JFS team was helpful and supportive, and their representative, Steve Best, visited our lab in January 2001. Since then, we have been following JFS development closely and upgrading our servers to support the latest versions.
The first installations of JFS were done on 1U rackmount units with Celeron 500MHz processors, 256MB of RAM and 20GB IDE disks. These units provided us with a working environment to test JFS and to experiment with its features using some of our applications. Since JFS version 1.0.0 was released in June 2001, we decided to install JFS on our test Linux platform, shown in Figure 2.
Our Linux systems are designed to serve short transaction-based requests. JFS provides a log-based, byte-level filesystem targeted for transaction-oriented systems, which makes it quite suitable for our type of systems.
The advantages of JFS from a telecom point of view are that it provides improved structural consistency, recoverability and much faster restart times than non-journaling filesystems, such as traditional UNIX filesystems. In most cases, the other filesystems are subject to corruption in the event of a system crash. They rely on restart-time utilities like fsck, which examines all of the filesystem's metadata to detect and repair structural integrity problems. This is a time-consuming and error-prone process; in a worst-case scenario, it can lose or misplace data. Telecom platforms cannot afford a process that prolongs a system's downtime.
With JFS, in case of a system failure, a filesystem is restored to a consistent state by replaying the log and applying log records for the appropriate transactions. The recovery time associated with this log-based approach is much faster, because the replay utility examines only the log records produced by recent filesystem activity, rather than examining all filesystem metadata.
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.
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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