chvdisk

Use the chvdisk command to modify the properties of a volume, such as the disk name, I/O governing rate, or unit number. You can also change Easy Tier settings.

Syntax

chvdisk { -namenew_name_arg | [ -cache { readwrite | readonly | none } [ -force ] ] | [ -ratethrottle_rate [-unitmb] ] | [ -udid vdisk_udid ] | { [ -warningdisk_size [ -unit { b | kb | mb | gb | tb | pb } ] ] | [ disk_size_percentage% ] } | [ { [ -copyid ] } ] | [ -autoexpand { on | off } [ { [ -copyid ] } ] ] | [ -primarycopy_id ] | [ -syncratesyncrate ] | [ -easytier { on | off } [ -copyid ] ] | [ -mirrorwritepriority { latency | redundancy } ] } { -volumegroup | { volumegroup | novolumegroup } } -novolumegroup -backupcloud [ { [ -enable -account { cloud_account_name | cloud_account_id } [ -backupgrainsize { 64 | 256 } ] ] | [ -disable ] } ] { vdisk_name | vdisk_id }

Parameters

-namenew_name_arg

(Optional) Specifies a new name to assign to the volume. You cannot use this parameter with the -rate or -udid parameters. This parameter is required if you do not use the -rate or -udid parameters.

Note: Do not use this parameter with file system volumes.

-cachereadwrite | readonly | none

(Optional) Specifies the caching options for the volume. Valid entries are:

Use readwrite to enable the cache for the volume.
Use readonly to disable write caching and allow read caching for a volume.
Use none to disable the cache mode for the volume.

The default is readwrite.

-force

(Optional) The force parameter can be used only for changing the caching mode. Use the force parameter with the cache parameter to specify that you want the system to change the cache mode of the volume even if the I/O group is offline. This option overrides the cache flush mechanism.

Attention: If the force parameter is used for changing the caching mode, the contents of the cache are discarded and the volume might be corrupted by the loss of the cached data. This corruption might occur if the system is able to destage all write data from the cache or not. Use the force parameter with caution.

Important: Using the force parameter might result in a loss of access. Use it only under the direction of IBM support personnel.

-ratethrottle_rate-unitmb

(Optional) Specifies the I/O governing rate for the volume, which caps the amount of I/O that is accepted. The default throttle_rate units are I/Os. By default the throttle_rate is disabled. To change the throttle_rate units to megabits per second (MBps), specify the -unitmb parameter. The governing rate for a volume can be specified by I/Os or by MBps, but not both. However, you can set the rate to I/Os for some volumes and to MBps for others. When the input/output operations per second (IOPS) limit is configured on a volume, and it is smaller than 100 IOPS, the throttling logic rounds it to 100 IOPS. Even if throttle is set to a value smaller than 100 IOPs, the actual throttling occurs at 100 IOPs.

Note: To disable the throttling on a specific volume, set the throttle_rate value to zero.

You cannot use this parameter with the -name or -udid parameters.

-udidvdisk_udid

(Optional) Specifies the unit number (-udid) for the disk. The vdisk_udid is an identifier that is required to support OpenVMS hosts; no other systems use this parameter. Valid options are a decimal number in the range 0 - 32,767, or a hexadecimal number from 0 to 0x7FFF. A hexadecimal number must be preceded by 0x (for example, 0x1234). If you do not use the -udid parameter, the default -udid is 0.

You cannot use this parameter with the -name parameters.

-warningdisk_size | disk_size_percentage%

(Optional) Generates a warning when the used disk capacity on the thin-provisioned copy first exceeds the specified threshold. You can specify a disk_size integer, which defaults to MBs unless the -unit parameter is specified; or you can specify a disk_size%, which is a percentage of the volume size. To disable warnings, specify 0 or 0%.

-unitb | kb | mb | gb | tb | pb

(Optional) Specifies the data units to use for the -warningdisk_size parameter. The default unit value is MB.

-autoexpandon | off

(Optional) Specifies whether thin-provisioned volume copies automatically expand their real capacities by allocating new extents from their storage pool. To use this parameter, the volume must be thin-provisioned.

-copyid

(Optional) Specifies the copy to apply the changes to. You must specify this parameter with the -autoexpand or -warning parameter. The -copy parameter is required if the specified volume is mirrored and only one volume copy is thin-provisioned. If both copies are thin-provisioned and the -copy parameter is not specified, the specified -autoexpand or -warning parameter is set on both copies.

-primarycopy_id

(Optional) Specifies the primary copy. Changing the primary copy takes effect only when the new primary copy is online and synchronized. If the new primary is online and synchronized when the command is issued, the change takes effect immediately. You cannot change the volume's primary copy if that primary copy has its autodelete flag is set to yes (on).

Important: You cannot use this parameter with a volume that is fast formatting.

-syncratesyncrate

(Optional) Specifies the copy synchronization rate. A value of zero (0) prevents synchronization. The default value is 50. See Relationship between the syncrate value and the data copied per second for the supported -syncrate values and their corresponding rates. Use this parameter to alter the rate at which the fully allocated volume or mirrored volume format before synchronization.

-easytieron | off

(Optional) Enables or disables the Easy Tier function.

Attention: Thin-provisioned and compressed volumes in a data reduction pool always have Easy Tier on, regardless of the pool setting.

-mirrorwriteprioritylatency | redundancy

(Optional) Specifies how to configure the mirror write algorithm priority. A change to the mirror write priority is reflected in the volume's view immediately and in the volume's behavior after all prior input and output (I/O) completes.

Choosing latency means a copy that is slow to respond to a write I/O becomes unsynchronized, and the write I/O completes if the other copy successfully writes the data.
Choosing redundancy means a copy that is slow to respond to a write I/O synchronizes completion of the write I/O with the completion of the slower I/O to maintain synchronization.

-volumegroupvolumegroup_name | volumegroup_id

(Optional)

Specifies a new volume group for a volume. This parameter is mutually exclusive with -novolumegroup.

-novolumegroup

(Optional) Specifies that a volume does not belong in any volume group. This parameter is mutually exclusive with -volumegroup.

-backupcloud

(Optional) Specifies the cloud snapshot type to enable or disable. The value must be cloud.

-enable

(Optional) Enables the backup or snapshot type that is specified with the -backup parameter.

-disable

(Optional) Disables the backup or snapshot type that is specified with the -backup parameter.

-accountcloud_account_id | cloud_account_name

(Optional) Specifies the cloud account to use for the volume. You must specify -enable with this parameter.

-backupgrainsize64 | 256

(Optional) Specifies the grain size (in KB) for volume mappings. The values are 64 and 256. You must specify -enable to use this parameter.

You can enable a volume for a cloud snapshot with one account. You cannot enable cloud backup on a volume for a second time on the same or different cloud account.

You cannot turn off the cloud snapshot function if a snapshot in progress. Any snapshot that is in progress must complete or be canceled.

vdisk_name | vdisk_id

(Required) Specifies the volume to modify, either by ID or by name.

Description

The chvdisk command modifies a single property of a volume. To change the volume name and modify the synchronization rate, for example, you must issue the command twice. If the volume is offline, use recovervdisk command to recover the volume and bring it back online.

Important: To change the caching I/O group for a volume or preferred node, use the movevdisk command.

A thin-provisioned or compressed copy that is in a data reduction storage pool must enable -autoexpand. If a volume contains a copy that is in a data reduction storage pool, the cache mode must be set to readwrite.

A thin-provisioned or compressed copy that is in a data reduction storage pool cannot have a warning threshold set. To change the warning threshold, you must specify the -copy.

You can specify a new name or label. Then, you can use the new name to refer to the volume.

You can set a limit on the number of I/O transactions that is accepted for this volume. It is set in terms of I/Os per second or MBs per second. By default, no I/O governing rate is set when a volume is created.

Attention: All capacities, including changes, must be in multiples of 512 bytes. An error occurs if you specify a capacity that is not a multiple of 512, which can happen only when byte units are used. The default capacity is in MB.

When the volume is created, no throttling is applied to it. Use the -rate parameter to change it. To change the volume back to an unthrottled state, specify 0 (zero) with the -rate parameter.

For thin-provisioned and compressed volume copies in data reduction pools, the Easy Tier status is derived from the data reduction pool as the data is managed by a central data disk. Therefore, the Easy Tier mode cannot be turned off on these volume types. The thin-provisioned and compressed volumes in a data reduction pool always have Easy Tier on, regardless of the pool setting. The Easy Tier setting is a combination of pool and volume setting, as detailed in a table in the help for mkvdisk. Leaving easy tier always on for the volume allows the pool setting to be the one that switches it on or off. For fully allocated volumes in a data reduction pool, Easy Tier can be turned both on and off.

The rate at which the volume copies resynchronize after loss of synchronization can be specified by using the -syncrate parameter. This table provides the relationship of the syncrate value to the data copied per second.

Note: These settings also affect the initial rate of formatting.

Table 1. Relationship between the `syncrate` value and the data copied per second
User-specified `syncrate` 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