Last year, Microsoft released version 2.0 of its free iSCSI initiator package, the software that allows Windows servers to make use of inexpensive iSCSI storage arrays by mounting remote volumes that appear local to the server.
Like fibre channel SANs, iSCSI SANs provide significant flexibility and offer data protection benefits not inherent with direct attached storage. Until the release of the 2.0 version of the iSCSI initiator, Microsoft's solution was less than ideal for high-performance, high-availability environments, unless third party software was used.
The 2.0 initiator adds a number of features that make Microsoft's software useful for high-end applications:
- MPIO (Multipath I/O): Under previous versions of Microsoft's initiator, MPIO--one way for iSCSI to achieve high availability--was only available by installing a DSM add-on from the hardware vendor. A DSM is a Device Specific Module that assists in achieving desired reliability, but also adds some complexity to the overall solution as you often have to match versions of the DSM against specific older versions of the initiator. Native MPIO support is included in version 2.0 of Microsoft's initiator.
- MCS (Multiple Connections per Session): This is the same as MPIO, except load balancing policies are applied to all LUNs exposed to the session; whereas, under MPIO, policies apply to individual disks.
- IPv6 support: Probably not an important enhancement, but good for the future (maybe...).
- 64-bit support: As you would expect by now, version 2.0 offers support for 64-bit processors, operating systems, and applications. The iSCSI initiator is currently included in all builds of the upcoming Vista operating system.
- Better error recovery, making the initiator more suited for tape backup scenarios.
It's highly recommended that you uninstall previous versions of the initiator before you install the latest version.
The Microsoft iSCSI Initiator works under Windows 2000 SP4 or higher, Windows XP SP1 or higher, and Windows Server 2003 or higher.
A reminder for those installing version 2.0 of the initiator
In a tip I wrote last year, I
told you about a problem that you
might face when using an iSCSI array to house file shares. I want to
reiterate that advice here as I've seen dozens of messages on various forums
from people suffering from this problem. If you don't take steps to change
service dependencies, when you create shares, they will seem to disappear each
time you reboot the server.
To avoid this problem, from a command prompt, type sc config LanManServer depend=MSiSCSI and press [Enter]. This will force the LanManServer service to wait for the iSCSI initiator service before starting, which will keep your shares intact.
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