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Storage over IP and TCP/IP offload - Part Two

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How is SAN storage dynamically configured in a Microsoft environment? How does the OS attach the storage once it is zoned and reachable by that MS server?

In reviewing my previous response, I realize that I did not answer your question directly. Instead, I referred to the attachment of a virtualized SAN volume. Additional input on this subject was just provided to me by Bruce Naegel, Senior Product Manager at Veritas Corporation."In a Windows 2000 or NT SAN environment, RAID storage can be added to a server using a variety of methods:

A. Creating a new LUN on a storage system that is already connected to the server (e.g. the storage system and the server are in the same zone).

B. Exposing a LUN that was previously created by connecting the LUN to an output port on the RAID system. This function can be called "port mapping" or path creation and is usually found on larger disk subsystems. Using this function assumes the port on the RAID system in question is already in the zone.

C. Taking a new storage system and adding it (with its new LUNs) to the zone containing the server.

Once the storage is connected, it needs to be made visible to the server by a rescan performed by Disk Administrator (NT 4.0) or LDM (Logical Disk Manager, Windows 2000).

A rescan using NT 4 Disk Administrator is performed by closing Disk Administrator and restarting it. LDM under Windows 2000 has the ability to do a rescan from the Action menu. Note that presenting a new LUN can be performed without the need to reboot the NT or Windows 2000 server. Most customers like to separate Windows environments and UNIX environments into separate sections of a SAN.

In addition, Windows does not have a "mount" command limiting the disks that can be mounted on a SAN. Under certain conditions, especially with NT 4, each server may try to claim all the NT storage. To address this, one needs a tool to limit the visibility of each NT server to only see the storage assigned to it on a SAN.

One such method to limit the storage visible to an NT or Windows server is the use of LUN Binding or ACL (Access Control List) functions available in certain RAID storage systems. These functions of a RAID system make a LUN visible ONLY to the server or servers listed in the ACL (Access Control List).

Another method to address this issue is to create a zone containing one server and the storage assigned to that one server. Customers often ask if they can "grow" a LUN on line in the Windows environment. Under NT 4, one has to reboot the server to see the "enlarged" LUN. Alternately, one can present two LUNs and "glue" them together under Disk Administrator. This will present a larger LUN without the need to reboot the server.

Jon has more to say on this topic in Storage over IP and TCP/IP offload - Part Three.


This was first published in March 2001

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