Specifications

Escala Tower PL & S, E, T System Hardware
Chapter 3: External Storage and SAN Subsystems 76/116
9es3s1c3.doc
Rev 5.9
02/12/2003
6.1. Challenges and Risks
Designing a SAN looks like designing a LAN: it's a network, and the design must integrate analysis of
traffic requirements, the number and location of devices to connect, topology constraints, and other
network related factors. The design must also take into account the availability constraints, which are
much higher for storage access that for legacy LANs. A failure of a Fibre Channel switch must stop
tens of applications servers, no more able to access to their data.
It is necessary to understand the behavior of infrastructure equipment such as hub, switches, bridges,
and all the proprietary features implemented by hardware vendors to simplify interoperability, improve
reliability, and manage the infrastructure. This knowledge must be combined with a good
understanding of all the proprietary fail-over solutions supported by each server, disk array, tape
library, SAN infrastructure device and management software.
And unfortunately, the Fibre Channel technology is not yet enough mature to guarantee
interoperability between any device like for LAN technologies. Thus, the design must take into
account the qualified links, or certified interoperability which are published by all the SAN vendors,
including Bull.
The last risk is that many equipment and software (like operating systems for servers) have not yet
integrated the SAN dimension. They still behave like with private SCSI storage, trying to discover all
the storage resources, our writing on disks when they recognize an OS compatible format (like NT
servers do). Sharing storage resource in heterogeneous server environment must be carefully analyzed
and managed.
6.2. SAN Management
The SAN management covers specific aspects, which were not covered by previous storage
management tools:
•
SAN infrastructure (hub, switches, bridges, …)
•
Resource sharing.
Managing a SAN infrastructure is very similar to managing a LAN. It involves hubs, switches, bridges
and any other device that is part of the network infrastructure; topology analysis, link status, the
management of virtual networks (using zoning), and the monitoring of data flow, performance metrics,
QOS, availability, etc. But SAN infrastructure products available on the market are less numerous than
the ones for LAN technology. This is because it's a new technology, standards are not well defined and
hardware vendors are relatively small and none of them is able to provide a hardware/software global
solution.
The management of resource sharing is also critical to enable a safe operation within SAN
environments. A SAN enables each server to access each tape drive or disk logical volume attached to
it. It is very flexible, but very complex for the server administrators, because they may have to manage
hundreds of resources, duplicated on all the application servers. That's why it is critical, even in small
size SANs (less than 8 servers) to deploy management tools that control resource sharing. And again,
there is not yet a global solution. Tape drive allocation and sharing is usually managed by the backup
software, which must integrate specific SAN features.