Veritas Cluster Server Bundled Agents Reference Guide
Veritas⢠Cluster Server Bundled Agents Reference Guide - Symantec Veritas⢠Cluster Server Bundled Agents Reference Guide - Symantec
24 Storage agents DiskReservation (DiskRes) agent ■ Use the Volume Manager Diskgroup (VMDg) and MountV agents to provide high availability for shared disks and volumes managed using Storage Foundation for Windows. In case of a NetApp storage environment, the Logical Unit Numbers (LUNs) on the NetApp Filer are made highly available by the NetApp Filer and NetApp SnapDrive agents instead of the VMDg and MountV agents respectively. See “About hardware replication agents for NetApp” on page 161. DiskReservation (DiskRes) agent The DiskReservation agent monitors shared disks. The agent also prevents data corruption caused by network partitioning, a condition in which two cluster systems provide the same services simultaneously. This condition occurs due to network link failure and may cause data corruption. The agent ensures only one cluster system holds persistent reservation to shared disks. During a typical network partition, one system (SystemA) has the DiskRes resource online and holds reservation to shared disks. Another system (SystemB) attempts to come online and reserve the shared disks. To avoid network partitioning, SystemB issues a bus reset and waits for the interval specified in the GracePeriod attribute to determine if SystemA is functioning. If SystemA is functioning, SystemA reacquires reservation to the shared disks. Otherwise, SystemB attempts to reserve the shared disks. The system that gains reservation to the disks is designated owner of the resource, and the resource is brought online on that system. By default, a system is designated owner of the resource if it reserves 80 percent of the shared disks. You can modify the agent's configuration to change the ownership criteria. Note: This agent is not supported in an SFW environment. Agent functions online offline monitor Reserves the shared disks each second. Releases the reservation to the shared disks. Verifies the system holds the reservation to the shared disks.
Storage agents DiskReservation (DiskRes) agent 25 State definitions ONLINE OFFLINE UNKNOWN Indicates the system holds the reservation to the shared disks. Indicates the system does not hold the reservation to the shared disks. Indicates the agent could not determine the status of the shared disks. Resource type definition type DiskRes ( static i18nstr ArgList[] = { Signatures, ConfigPercentage, FailFastInterval, GracePeriod } str Signatures[] int ConfigPercentage = 80 int FailFastInterval = 1 int GracePeriod = 5 ) Attribute definitions This section summarizes the required and optional attributes of the DiskRes agent. Table 2-1 DiskRes agent required attributes Required Attribute Signatures Description An array specifying the signature of each SCSI disk. To retrieve the disk signature, use the VCS utility, "havol" with the "scsitest" option. See the VCS Administrator's Guide for instructions on how to use the utility. Type and Dimension: string-vector
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24<br />
Storage agents<br />
DiskReservation (DiskRes) agent<br />
■<br />
Use the Volume Manager Diskgroup (VMDg) and MountV agents to provide<br />
high availability for shared disks and volumes managed using Storage<br />
Foundation for Windows.<br />
In case of a NetApp storage environment, the Logical Unit Numbers (LUNs) on<br />
the NetApp Filer are made highly available by the NetApp Filer and NetApp<br />
SnapDrive agents instead of the VMDg and MountV agents respectively.<br />
See “About hardware replication agents for NetApp” on page 161.<br />
DiskReservation (DiskRes) agent<br />
The DiskReservation agent monitors shared disks. The agent also prevents data<br />
corruption caused by network partitioning, a condition in which two cluster<br />
systems provide the same services simultaneously. This condition occurs due to<br />
network link failure and may cause data corruption. The agent ensures only one<br />
cluster system holds persistent reservation to shared disks.<br />
During a typical network partition, one system (SystemA) has the DiskRes resource<br />
online and holds reservation to shared disks. Another system (SystemB) attempts<br />
to come online and reserve the shared disks. To avoid network partitioning,<br />
SystemB issues a bus reset and waits for the interval specified in the GracePeriod<br />
attribute to determine if SystemA is functioning. If SystemA is functioning,<br />
SystemA reacquires reservation to the shared disks. Otherwise, SystemB attempts<br />
to reserve the shared disks. The system that gains reservation to the disks is<br />
designated owner of the resource, and the resource is brought online on that<br />
system.<br />
By default, a system is designated owner of the resource if it reserves 80 percent<br />
of the shared disks. You can modify the agent's configuration to change the<br />
ownership criteria.<br />
Note: This agent is not supported in an SFW environment.<br />
Agent functions<br />
online<br />
offline<br />
monitor<br />
Reserves the shared disks each second.<br />
Releases the reservation to the shared disks.<br />
Verifies the system holds the reservation to the shared disks.
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