Creating a virtual disk–Set attributes: Panel help

You can set attributes for a virtual disk (VDisk) on the Set Attributes panel in the Create Virtual Disk wizard in the SAN Volume Controller Console. You can choose to create a striped or sequential disk, select a method for caching data, and set other attributes related to the VDisk that you are creating.

Fields

You can update the following fields:

Select the type of virtual disk

Select the type of VDisk to create. The following values are possible:

Striped: Select this type if you want the VDisk to have data that is striped across multiple managed disks (MDisks).
Sequential: Select this type if you want the VDisk to have data that is stored sequentially on a single MDisk.

Select the cache mode

Select the type of cache mode to use for the VDisks. The following values are possible:

Read/Write: Indicates that all read and write I/O operations that are performed by the VDisk are stored in the cache.
None: Indicates that all read and write I/O operations that are performed by the VDisk are not stored in the cache.

Unit device identifier

Enter a unit device identifier for the VDisks. This field is used only by hosts that are using the OpenVMS operating system. For other operating systems, setting a unit device identifier is not required.

Specify the number of virtual disks (1 - 2048) to create

Enter the number of VDisks to create. Valid values are 1 - 2048.

Space-efficient

Select this option to create a space-efficient VDisk. The following options are available:

VDisk Capacity

Enter the virtual capacity of the VDisk that is presented to hosts. Virtual capacity is the amount of storage that is available to a server on a VDisk copy. In a space-efficient VDisk, the virtual capacity can be different from the real capacity. In a standard virtual disk, the virtual capacity and real capacity are the same. The virtual capacity provides the total amount that can be further allocated to VDisk copies. The following units can be selected:

Warn when used capacity of VDisk reaches

Specify a threshold to send a warning message for the VDisk when the real capacity that is used first exceeds the specified level. You can either specify a percentage of total VDisk capacity or enter a specific amount of capacity for the threshold.

Note: If you specify a fixed value for the warning threshold, it is saved as a percentage. Therefore, when you view the warning level, it is displayed as a percentage.

If you enter a specific amount, you must also select the units for the used capacity. The following units can be selected:

If you select Autoexpand, the default value for the warning level is 80% of the VDisk's virtual capacity. If Autoexpand is not selected, the default value for warning is 80% of the total capacity. To disable warnings, specify 0 or 0%.

Autoexpand

Select this option if you want the space-efficient copies to automatically expand their real capacity by allocating new extents from their MDisk groups. Setting a space-efficient real capacity protects the copy from going offline when its MDisk group runs out of capacity. The real capacity is then expanded as the capacity is used. During this process, a fixed amount of unused real capacity is maintained. This amount is known as the contingency capacity. When you create a space-efficient VDisk, the contingency capacity is initially set to the same amount as the real capacity. If you manually change the real capacity, the contingency capacity becomes the difference between the used capacity and the new real capacity.

Grain size

Select the grain size in kilobytes (KB) for a copy of the space-efficient VDisk. The following values are possible:

Mirrored disk

Select this option if you want the VDisk to have mirrored copies. If the VDisk that you are creating uses Solid State Drives (SSDs) that reside inside the node, then the data that is stored on the VDisk is not protected against SSD or node failures. To avoid data loss, add a VDisk copy that uses SSDs inside another node. The following options are available:

Synchronization Rate

Enter the copy synchronization rate. A value of zero (0) prevents synchronization. The default value is 50 (2 MB per second).

The following table shows the relationship of the rate value to the data copied per second.

Table 1. Relationship between the *rate* value and the data copied per second
User-specified rate attribute value	Data copied/sec
1 - 10	128 KB
11 - 20	256 KB
21 - 30	512 KB
31 - 40	1 MB
41 - 50	2 MB
51 - 60	4 MB
61 - 70	8 MB
71 - 80	16 MB
81 - 90	32 MB
91 - 100	64 MB

Create copies in synch

Select this option to create synchronized copies. Select this option when MDisks are already formatted or when read stability to unwritten areas of the VDisk is not required.

Format VDisk before use (write zeros to its managed disk extents)

Select this option to format the VDisk before it is used.

Actions

The following actions are available:

Back: Click this button to return to the previous wizard panel.
Next: Click this button after you have completed this panel.
Cancel: Click this button to exit this wizard without creating the VDisk.