Database Reference
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provided to SQL Server. This is especially important for business-critical production
databases. It is fine to use Thin or Thick Lazy Zero for your Windows OS disk, while
using Eager Zero Thick for your database drives (data files, Temp DB, and transaction
logs). When using SQL AlwaysOn Failover Cluster Instance, it is recommended that you
configure Windows OS disks as Eager Zero Thick; shared LUNs will in this case be
configured as physical RDMs.
Figure 6.13 shows a sample configuration of a virtual disk with the selection of Thick
Provision Eager Zeroed.
Figure 6.13 New virtual disk—Thick Provision Eager Zeroed.
Using Raw Device Maps for SQL Server
A Raw Device Map (RDM), as the name suggests, is a direct mapping of a physical
LUN to a virtual machine. The main reason to choose RDM is SQL Server Failover
Cluster Instances (FCI). SQL FCI uses Windows Failover Clustering (previously known
as Microsoft Cluster Services), shared SCSI bus, shared disks between nodes, and
requires persistent SCSI reservations. To allow the persistent SCSI reservations and the
cluster to function correctly, Physical Mode or Pass-through RDM (pRDM) are
required. Another reason to consider using RDMs for SQL Server is if you are
 
 
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