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External storage must support SCSI-3 PR.
Volume should be configured by LUN(Logical Unit Number) unit. Partitioned volume in a LUN is not supported.If use PrType 3, at least 1GByte LUN is needed for key reservation.

Types of Shared disk resource

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2. 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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Configuration

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.

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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 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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[Figure] Shared disk and SCSI Lock resource configured in same LUN (PrType=1)2. Shared disk and SCSI lock resource is configured with different LUN (PrType=3)

At this type, shared disk agent manages DATA-DISK where user data is stored and SCSI lock agent uses exclusive LUN for key reservation. Therefore, two LUNs is required at least.
Lock-disk volume is created for 1:1 dependency with shared disk agent like a figure below.
By using multiple shared disk agents, and one SCSI reservation agent, you can configure the dependency relationship for use.
The storage capacity of this disk can be small because it is used to check the node that can access the storage.
By setting the dependency between the SCSI reservation resource and the shared disk resource, you can prevent damages to DATA-DISK caused by Split-Brains and so on. 

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[Figure] Shared disk and SCSI Lock resource is configured with different LUN( PrType=3)



Info

DATA-DISK 

  • It is a disk created by using a shared disk agent. It represents a disk where the actual user data is used.  

LOCK-DISK

  • It is a disk created by using a SCSI reservation agent.
    This is the disk that depends on DATA_DISK used in the shared disk when linking a shared disk agent.

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1. Shared disk and SCSI Lock resource is configured in same LUN (PrType = 1)

[Figure] Shared disk and SCSI Lock resource configured in same LUN

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  1. Install MCCS on both nodes
  2. Set group
  3. Add shared disk resource
  4. Enable shared disk resource and check offline on both nodes
  5. Add SCSI Lock resource (Select device path that created shared disk resource)
  6. Enable SCSI Lock resource and check key in resource attribute of MCCS web console.
  7. Configure dependency of resources (SCSI Lock resource must go online first)
  8. Test failover from node 2 to 1 
  9. Test failover from node 1 to 2
  10. Set application that customer uses

2.Shared disk and SCSI Lock resource configured with different LUN (PrType = 3)

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[Figure] Shared disk and SCSI Lock resource configured with different LUN

Registration Procedures 

First, register shared disk agent according to the procedure and after check if it works normally, check disk of SCSI Lock agent.  

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Adding

There are two way to add a resource which one is select this from a group name and another is select this from a resource type.

Adding in Group

Adding

Add the SCSI reservation application resource to a group.
Before configuring the SCSI reservation resource, you must configure the volume in advance by using the SCSI3 supporting storage.  

  1. When add a resource from a group name, select a group → right click → 'Add Resource'. 
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    [Figure] Adding Resource in a group

  2. Select 'SCSILOCK' from Resource Type lists and click 'Next' button. 
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    [Figure] Select Resource Wizard View
  3. Next steps are same as adding in resource type.

Adding in Resource Type


  1. ResourceType → Right Click → Click Add Resource
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    [Figure] Adding Resource in a resource type
     If all the information is retrieved, you can select a device path used as the SCSI reservation resource.

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    [Figure] Selecting driver letter View
    When there is no disk for SCSI Lock resource, "Disk Not Found" message appears.
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    [Figure] Disk Not Found
     If you select a device path used for the SCSI reservation resource, a name will be automatically recommended.


    [Figure] Select device pathSCSI Reservation Resource Added

  2. Click the 'Finish' and SCSI Lock resource is added.
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    [Figure] Adding SCSI Lock resource is completed
    button to add the SCSI reservation resource.
    You can immediately check the result in the management web console.


Deleting

Select resource type → right click → delete resource.

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The deleted resource will immediately disappear from the management web console.

Status

The following table explains the status switching of the MCCS resource caused by a user's command and the status.
The command assumes that it is generated by a user.

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StatusAgent commandDescriptionNote

Online

Disk key is exclusively reserved at an online node.
You cannot register a key at another node.

Offline

It ignores the reservation key stored. It first creates a new reservation key and switches to offline while maintaining the reservation.

 
Monitoring

Compares the key reserved in the disk and check if there is a reservation made on the disk.

 

Offline

1. Disk is reserved but the resource is still offline.
2. The actual offline state where the other node acquired a reservation.

Online

Register a key for a disk reservation and wait for a response from the other node.

 After going online once, the other node reservation is stolen. This is called preempt.

 
Monitoring

Compares the key reserved in the disk and check if there is a reservation made on the disk.

 

Trouble

It occurs when a reservation is stolen while going online.

Online

Register a key for a disk reservation and wait for a response from the other node.

After going online once, the other node reservation is stolen. This is called preempt.

 
OfflineIt ignores the reservation key stored. It first creates a new reservation key and switches to offline while maintaining the reservation. 

 

 

Attribute

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[Figure] SCSI Lock Attribute view

SCSI Lock resource provides the following detailed attributes as well.
Setting are available in "Resource Unique Attribute" in resource's attribute tab.
Each attribute value has the following meanings:

Display the unique attribute of SCSI reservation resource. 

Attribute

Description

Data Type

DefaultEditNote
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.

STRING2 timesO 
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 but MCCS uses 1 5 (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.

Registor Only).

STRING

Prytpe = 15O 

 

 

scsicmd Command

Syntax

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