Increase Performance, Reliability and Capacity with Software RAID
In addition to creating and rebuilding arrays, you need to be familiar with a few other tasks. It is important to understand how to start and stop arrays. Run the following commands to unmount and stop the RAID 1 array you created earlier:
# umount /dev/md0 # mdadm -S /dev/md0 # cat /proc/mdstat
As you can see, the array no longer is listed in /proc/mdstat. In order to start your array again, you need to assemble it (there isn't a start command). Run the following commands to assemble and remount your array:
# mdadm -As /dev/md0 # mount /dev/md0 # cat /proc/mdstat
Sometimes it's useful to place an array in read-only mode. Before you do this, you need to unmount the filesystem (you can't just remount as read-only). If you try to place an array in read-only mode while it is mounted, mdadm will complain that the device is busy:
# umount /dev/md0 # mdadm -o /dev/md0 # cat /proc/mdstat # mount /dev/md0
Notice how /dev/md0 is now read-only, and the filesystem was mounted as read-only automatically. Run the following commands to change the array and filesystem back to read-write mode:
# mdadm -w /dev/md0 # mount -o remount,rw /dev/md0
mdadm can be configured to send e-mail notifications regarding the status of your RAID arrays. Ubuntu automatically starts mdadm in monitoring mode for you; however, it currently is configured to send e-mail to the root user on the local system. To change this, edit /etc/mdadm/mdadm.conf and set MAILADDR to your e-mail address, then restart the mdadm dæmon:
# vim /etc/mdadm/mdadm.conf
Set MAILADDR to <your e-mail address>, and then do:
# /etc/init.d/mdadm restart
Run the following command to test your e-mail notification setup:
# mdadm --monitor --scan -t -1
If you are building a new server, you can use the Ubuntu Alternate install CD to set up your system on a software RAID array. If you don't have the luxury of performing a clean install, you can use the following process to convert your entire server to a RAID 1 array remotely. This requires your server to have an additional drive that is the same size or larger than the first disk. These instructions also assume you are using the server edition of Ubuntu 8.04 (Hardy), but the process is similar in other Linux distributions. You always should test a procedure like this before performing it on a production server.
Install mdadm and verify that the software RAID kernel module was loaded properly:
# apt-get install mdadm # cat /proc/mdstat
Copy the partition table from your first drive to your second drive, and set the partition types to “Linux RAID autodetect”:
# sfdisk -d /dev/sda | sfdisk /dev/sdb # fdisk /dev/sdb > t > 1 > fd > t > 2 > fd > w
Create the RAID 1 arrays for the root and swap partitions, and update the mdadm configuration file. This time, specify that the first drive is “missing”, which will delay the rebuild until you add the first drive to the array. You don't want to mess with the first drive until you are sure the RAID configuration is working correctly:
# mdadm -C /dev/md0 -n2 -l1 missing /dev/sdb1 # root # mdadm -C /dev/md1 -n2 -l1 missing /dev/sdb2 # swap # cat /proc/mdstat # mdadm --detail --scan >> /etc/mdadm/mdadm.conf
Modify /boot/grub/menu.lst so your server boots from the array:
# vim /boot/grub/menu.lst
Add fallback 1 to a new line after default 0.
Change the kopt line to # kopt=root=/dev/md0 ro.
Copy the first kernel entry and change (hd0,0) to (hd1,0).
Change root=xxx to root=/dev/md0 in the new kernel entry.
When your server is booting up, it needs to be able to load the RAID kernel modules and start your array. Use the following command to update your initrd file:
# update-initramfs -u
At this point, you can create and mount the filesystem, then copy your data to the additional drive. Make sure all of your applications are shut down and the server is idle; otherwise, you run the risk of losing any data modified after you run the rsync command:
# mkswap /dev/md1 # mkfs.ext3 /dev/md0 # mkdir /mnt/md0 # mount /dev/md0 /mnt/md0 # rsync -avx / /mnt/md0
To mount the RAID arrays automatically when your server reboots, modify /mnt/md0/etc/fstab and replace /dev/sda1 with /dev/md0, and replace /dev/sda2 with /dev/md1. You do this only on the second drive, in case you need to fall back to the old setup if something goes wrong:
# vim /mnt/md0/etc/fstab
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.
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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