Two basic mechanisms help to accomplish this goal: the
quorum database (explained shortly) and the ongoing network heartbeat between the
nodes. Windows Server 2003 and SQL Server 2005 also provide a more granular means
of failover: mount points.
CHAPTER 7 n CLUSTERING 176
???SHARED??? STORAGE
A number of devices can qualify as ???shared??? storage, including a network share, network-attached
storage (NAS), a SAN, or an external SCSI disk array. I??™ve even encountered shared storage as a virtual
drive shared by two virtual servers on the same physical server (more on hardware virtualization in
Chapter 10).
For the purposes of Windows clustering, the only valid forms of shared storage are either a SAN or
an external SCSI cabinet. You can get clustering to work in other configurations, but given how sensitive
clustering is when it comes to hardware, using any other technique would bring a world of pain.
Keep in mind that Windows clustering also uses nonshared storage; each server must have its
own local hard drive. It can be easy to accidentally place data that should be shared onto a local drive
instead.
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