Use Linux as a SAN Provider
Another feature often run with iSCSI is multipathing. This allows Linux to use multiple networks at once to access the iSCSI target. It usually is run on separate physical networks, so in the event that one fails, the other still will be up and the initiator will not experience loss of a volume or a system crash. Multipathing can be set up in two ways, either active/passive or active/active. Active/active generally is the preferred way, as it can be set up not only for redundancy, but also for load balancing. Like Fibre Channel, multipath assigns World Wide Identifiers (WWIDs) to devices. These are guaranteed to be unique and unchanging. When one of the paths is removed, the other one continues to function. The initiator may experience slower response time, but it will continue to function. Re-integrating the second path allows the system to return to its normal state.
When working with local disks, people often turn to Linux's software RAID or LVM systems to provide redundancy, growth and snapshotting. Because SAN volumes show up as block devices, it is possible to use these tools on them as well. Use them with care though. Setting up RAID 5 across three iSCSI volumes causes a great deal of network traffic and almost never gives you the results you're expecting. Although, if you have enough bandwidth available and you aren't doing many writes, a RAID 1 setup across multiple iSCSI volumes may not be completely out of the question. If one of these volumes drops, rebuilding may be an expensive process. Be careful about how much bandwidth you allocate to rebuilding the array if you're in a production environment. Note that this could be used at the same time as multipathing in order to increase your bandwidth.
To set up RAID 1 over iSCSI, first load the RAID 1 module:
After partitioning your first disk, /dev/sdb, copy the partition table to your second disk, /dev/sdc. Remember to set the partition type to Linux RAID autodetect:
sfdisk -d /dev/sdb | sfdisk /dev/sdc
Assuming you set up only one partition, use the mdadm command to create the RAID group:
mdadm --create /dev/md0 --level=1 --raid-disks=2 /dev/sdb1 /dev/sdc1
After that, cat the /etc/mdstat file to watch the state of the synchronization of the iSCSI volumes. This also is a good time to measure your network throughput to see if it will stand up under production conditions.
Running a SAN on Linux is an excellent way to bring up a shared environment in a reasonable amount of time using commodity parts. Spending a few thousand dollars to create a multiterabyte array is a small budget when many commercial arrays easily can extend into the tens to hundreds of thousands of dollars. In addition, you gain flexibility. Linux allows you to manipulate the underlying technologies in ways most of the commercial arrays do not. If you're looking for a more-polished solution, the Openfiler Project provides a nice layout and GUI to navigate. It's worth noting that many commercial solutions run a Linux kernel under their shell, so unless you specifically need features or support that isn't available with standard Linux tools, there's little reason to look to commercial vendors for a SAN solution.
Michael Nugent has spent a good deal of his time designing large-scale solutions to fit into tiny budgets, leveraging Linux to fulfill roles that typically would be filled by large commercial appliances. Recently, Michael has been working to design large, private clouds for SaaS environments in the financial industry. When not building systems, he likes sailing, scuba diving and hanging out with his cat, MIDI. Michael can be reached at firstname.lastname@example.org.
|Using Salt Stack and Vagrant for Drupal Development||May 20, 2013|
|Making Linux and Android Get Along (It's Not as Hard as It Sounds)||May 16, 2013|
|Drupal Is a Framework: Why Everyone Needs to Understand This||May 15, 2013|
|Home, My Backup Data Center||May 13, 2013|
|Non-Linux FOSS: Seashore||May 10, 2013|
|Trying to Tame the Tablet||May 08, 2013|
- RSS Feeds
- Making Linux and Android Get Along (It's Not as Hard as It Sounds)
- New Products
- Drupal Is a Framework: Why Everyone Needs to Understand This
- A Topic for Discussion - Open Source Feature-Richness?
- Home, My Backup Data Center
- Validate an E-Mail Address with PHP, the Right Way
- Tech Tip: Really Simple HTTP Server with Python
- New Products
- Trying to Tame the Tablet
- git-annex assistant
5 hours 1 min ago
- direct cable connection
5 hours 24 min ago
- Agreed on AirDroid. With my
5 hours 34 min ago
- I just learned this
5 hours 38 min ago
6 hours 8 min ago
- not living upto the mobile revolution
9 hours 13 sec ago
- Deceptive Advertising and
9 hours 35 min ago
- Let\'s declare that you have
9 hours 36 min ago
- Alterations in Contest Due
9 hours 37 min ago
- At a numbers mindset, your
9 hours 38 min ago
Enter to Win an Adafruit Prototyping Pi Plate Kit for Raspberry Pi
It's Raspberry Pi month at Linux Journal. Each week in May, Adafruit will be giving away a Pi-related prize to a lucky, randomly drawn LJ reader. Winners will be announced weekly.
Fill out the fields below to enter to win this week's prize-- a Prototyping Pi Plate Kit for Raspberry Pi.
Congratulations to our winners so far:
- 5-8-13, Pi Starter Pack: Jack Davis
- 5-15-13, Pi Model B 512MB RAM: Patrick Dunn
- Next winner announced on 5-21-13!
Free Webinar: Linux Backup and Recovery
Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.
In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.