Interview

Expert Q&A: Putting Linux storage to work

Jan Stafford
What are good strategies for consolidating storage on a SAN?
The answer depends on the nature of the applications that utilize a customer's SAN infrastructure. If the applications are not real-time and will not need to scale a significant amount over the lifetime of the deployment, some customers have placed NAS (Network-Attached Storage) front-ends on their SAN architectures to get single-instance ease of management and data sharing benefits.

For high-transaction-oriented or highly scalable application environments on Linux (a la Linux server proliferation), customers have opted for high performance, robust and highly scalable cluster file system (CFS) solutions. The No. 1 benefit of this technology in a Linux SAN deployment is storage consolidation. What are the challenges of integrating Linux into an existing SAN environment?
Integrating Linux into a SAN environment is really no different than integrating in any other operating system into the SAN. You must be careful in ensuring that when defining the LUN (logical unit number) to the SAN that you understand the ramifications of enques and integrity with the logic volume defined. If you look at using the global file system and integrate Logical Volume Manager (LVM) and LVM2 into a SAN environment, you must take into account the intricacies of the underlying file system. Sistina does a great job of guiding you in the use of GFS (Global File System) on their Web site, and this could be a great jumping-off

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point. You also need to look at tools to manage the complete SAN environment, not just Linux. What are some commonly used Linux server architecture options for consolidating enterprise storage on a SAN?
In order to minimize floor space dedicated to Linux servers, companies have adopted two deployment strategies: densely packed IA-32/64 racked or blade based architectures or Linux mainframe virtual machines. Both these architectures heavily use cluster file system technologies for storage consolidation. How does a CFS foster efficient storage consolidation?
Without a general purpose CFS, SAN customers have to needlessly replicate storage for the purpose of sharing data between servers. Thus, if "N" servers are using the same data for the same workload, the data must be replicated "N" times! (And this replication is not for high availability, it is simply for data sharing.) This is cost prohibitive (if N is greater than, say, three), not because of the additional hardware expense, but because of the additional management overhead associated with system and storage management. Thus, a CFS gives consistent access of the storage pool -- a single system view of the SAN -- for all the Linux servers within a deployment thereby enabling data consolidation.

By the way, companies like Oracle, Red Hat, Sistina, IBM and SuSE and have dedicated a significant amount of resources to developing, testing and certifying Linux CSF solutions. What is the state of host bus adapter (HBA) support in Linux?
When building a SAN from the perspective of the server operating system, your first concern has to be focused on the Fibre Channel HBA hardware and drivers. Both Qlogic and Emulex provide solid device driver support for Linux for their full product lines (including both 1- and 2-GB speed adapters). Sistina has deployed large SANs on both Qlogic and Emulex drivers with good success, so this is something you can safely mark on your checklist. What file systems are supported in Linux on disk arrays from the major vendors?
Today, Ext2 and Ext3 file systems with journaling are the most widely supported, single-system file systems supported by the major vendors. Cluster file systems are now being tested and certified by Linux distributors, like SuSE and Red Hat, thanks to the growing importance of the SAN and clustered computing paradigms in the enterprise. What is the state of host bus adapter (HBA) support in Linux?
A little less than a year ago most Linux software providers spent most of their time debugging customers' SANs because of the minimal upfront Linux testing and certification done by many hardware suppliers. Today, that has changed completely. It is not uncommon to see that SAN solution providers (like EMC) certify HBAs first on Linux and Windows and then on others. The leading HBA suppliers have delivered stable Linux drivers for all the volume HBAs on all the leading distributions, yet another sign of the maturity of Linux in core enterprise markets. How can IT shops help convince independent software vendors (ISVs) to port their applications to Linux?
ISVs, like any other businesses, look at the economics of and their capabilities to meet new environments. When customers reach critical mass and the vendor can see that supporting Linux will fit their business model, then they will port it. Like any other effort, it requires a win-win for you and them. If you need (a particular application ported), you should contact your distribution vendor and have them add influence into an ISV's decision.


FOR MORE INFORMATION:

SearchEnterpriseLinux.com news exclusive: "Sistina execs: Linux-based SANs spell success"

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Users tell us that it's hard to find storage management software that supports Linux. Is there vendor activity in this area?
Storage vendors like IBM, BMC and StorageTek have significant storage management products for Linux. These companies, as well as Veritas and CA, all have deployed storage management software focused on enterprise Linux deployments.

Perception is that support may lag reality a bit, which is usually the case. As companies begin to focus not just on the technologies but on the marketing of these products, awareness will increase and all enterprises, not just the early adopters, will be able to deploy these storage management frameworks on Linux.


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