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Disk management function in software perspective (shared disk agent)
Disk management function in hardware perspective (SCSI Lock agent)
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22. Both the shared disk agent and the SCSI reservation agent can read and write data.
However, a SCSI reservation agent intends to protect the shared storage resource, so you are not recommended to use it alone to read and write data.
Thus, a SCSI reservation agent can be used together with a shared storage agent or can use a separate LUN from the shared storage (PrType option).
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SCSI-Lock resource can be configured in 2 ways with shared disk resource. Configuration process changes according to the attribute value of SCSI Lock resource.
1. When shared disk and SCSI Lock resource is configured with the same LUN (PrType=1)
When you define an attribute of SCSI Lock resource as PrType=1, you can configure shared disk and SCSI Lock resource with the same LUN.
SCSI Lock agent manages DATA-DISK(shared disk resource) using by MOUNT/UMOUNT command and manages LOCK-DISK(SCSI Lock resource) using by SCSI-3 PR as shown below.
By setting up the dependency between SCSI Lock resources and shared disk resources, any damage of data-disk can be prevented which may occur in such case like Split-Brain.
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Attribute | Description | Data Type | Default | Edit | Note |
| DevicePath | Define the device path of disk to be used for reservation. When register device path, DUID of connected disk will automatically obtain. | STRING | X | ||
| DiskDUID | DUID(Device Unique ID, 16 byte as Hex value) of disk is used as identifier. Specify DUID of reserve disk. This value is secure when DriveLetter atribute us specified. Try not to insert this value yourself. DUID information can be checked through scsicmd.cmd command and both nodes need to have the same value. | STRING | X | ||
| Key | MAC address is used as Reserved-Key. This key is automatically set by agent. | STRING | X | ||
| PreemptWaitCount | Time waiting for permission of other node before reservation Waiting time is (PreemptWaitCount * MonitorInterval) seconds. | STRING | 2 times | O | |
| PrType | This attribute decides on how to give the permission of reserve disk access as Persist Type specified in SCSI3-PR spec. There are 6 types bur MCCS uses 1 (Write Exclusive) or 3 (Exclusive Access). 1 (Write Exclusive) is used when same LUN is used with shared disk. 3 (Exclusive Access) is used when only Lock_Disk is used. In this case, SCSI Lock agent LUN is required. | STRING | Prytpe = 1 | O |
scsicmdCommandscsicmd Command
Syntax
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scsicmd [option] [devicePath] |
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This is the utility to use SCSI 3 PR command more easily. Following is the provided options.
Option | Description |
-c devicePath | It deletes Reserved-Key and Registered-Key of local node of disk. |
-cf devicePath | It forcely deletes Reserved-Key and Registered-Key of local node of disk. This is mostly used when access to disk is inavailable. |
| -r devicePath | Registers diskld-specified disk. |
-l devicePath | If node is yet to reserve, close the specified disk and reserve. |
-lf devicePath | It forcelu closes specified disk and reserve, even node has been reserved. Meaning, it takes over other reservation. |
| -h | It shows help of scsicmd |
no option | It shows the state information regarding disk reservation when there is no other option. |
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