Before enabling Continuous Data Protection (CDP) on a virtual
disk, see Continuous Data
Protection (CDP) for very important
notes and best
practices.In this topic:
Enabling/disabling CDP and changing settings
Changing the location and maximum size of the history log
Also see:
Virtual Disk Groups for information when performing rollback operations on groups.
System Health Thresholds to set history log size and retention period thresholds.
Create a rollback |
Creates a logical image of the data residing on a CDP-enabled virtual disk at a selected point in time. (After you create the rollback, you can perform additional operations on the rollback.) See Creating Rollbacks. |
Revert from rollback |
Resynchronizes the CDP-enabled virtual disk and the selected rollback, so that the CDP-enabled virtual disk becomes an image of the current state of the rollback. See Reverting from Rollbacks. |
Split rollback |
Terminates the relationship between the CDP-enabled virtual disk and the rollback virtual disk. The data on the rollback is preserved. After the operation is complete, the rollback virtual disk becomes a fully usable single virtual disk and is no longer designated as a rollback virtual disk. See Splitting Rollbacks. |
Delete rollback |
Deletes the rollback virtual disk and leaves the CDP-enabled virtual disk intact. See Deleting Rollbacks. |
Rollback operations can be performed from:
o The Virtual Disk Details page>Rollbacks tab.
o The context menu in the DataCore Servers Panel, Hosts Panel, or Virtual Disks List.
Before enabling Continuous Data Protection (CDP) on a virtual
disk, see Continuous Data
Protection (CDP) for very important
notes and best
practices.
CDP can be enabled when creating the virtual disk or any time after. The following instructions are for enabling or disabling the feature after the virtual disk is created.
Notes:
o Before enabling this feature or changing the settings, refer to Continuous Data Protection (CDP) to understand CDP and the settings. Settings can be changed at any time in the Virtual Disk Details page under the Settings tab.
o This feature is not supported for dual virtual disks or other types of virtual disks created from pass-through disks.
o CDP is not supported for use with these features and commands:
· The Continuous Data Protection (CDP) feature is not compatible with the Sequential Storage feature. Virtual disks can only be enabled for one of these features.
· Snapshots or rollbacks
· Pool repair (Purge Disk operation) or Move operations. Replace operations can be performed but CDP will not be enabled on the virtual disks.
o Enabling CDP is an intrusive operation that fails accesses to the virtual disk for a short time period. For this reason, a single virtual disk must be unserved before the feature is enabled. A mirrored virtual disk may be served, but one side will go down briefly.
o CDP only runs on one side of the virtual disk. Once CDP is enabled, any data updates are saved to the history log on the server running CDP; therefore, from that point, allocations are reflected in the history log instead of the storage source. Other storage sources in the virtual disk have data written directly to the storage and allocations are reflected for those storage sources. Allocations can be viewed in the Virtual Disk Details page>Info tab.
1 If enabling CDP on a single virtual disk, it must be unserved from hosts.
2 In the Virtual Disk Details page>Settings
tab, click Advanced Options.
(This operation can also be initiated using the context menu from the panels
and any virtual disk list.)
3 Select the Continuous Data Protection Enabled check box.
4 In DataCore Server and Disk Pool, select the DataCore Server and disk pool where the history log should be created.
5 In Maximum history log size, select the maximum log size.
6 Click Apply.
If the enabled virtual disk is mirrored, as data is received from the host, at times the allocation size of the virtual disk on the DataCore Servers may be different. This expected behavior when CDP is enabled.
Important Notes:
o When CDP is disabled for a virtual disk, all rollbacks created from the virtual disk will be deleted.
o CDP cannot be disabled for a virtual disk if rollbacks are served to hosts.
o Disabling CDP can take
a considerable amount of time. The progress can be monitored on the Virtual Disk Details page>Info
tab. 
To disable CDP after virtual disk creation:
1 In the Virtual Disk Details page>Settings tab, click Advanced Options.
2 Clear the Continuous Data Protection Enabled check box.
3 Click Apply.
A rollback is a logical copy of a CDP-enabled virtual disk created at a chosen point-in-time (restore point). Rollbacks can be created at various restore points, served to hosts and viewed to determine the validity of the data. The rollback containing the optimal image of data can be used to restore the lost or damaged data.
Important:
o Before creating rollbacks, refer to Continuous Data Protection (CDP) for important information about how the history log affects rollbacks.
o The best practice is to create a rollback when data is in a known good state. If possible, before creating rollbacks, perform an application-specific flush and quiesce for consistent data, then pause I/O on the application until after the rollbacks are created.
o Persistent rollbacks will prevent destaging of the history log past the restore point and therefore cause the history log to grow and consume unexpected amounts of pool resources. To prevent this, stop the host I/O to the CDP-enabled virtual disk until the rollback is deleted or split.
o Rollbacks cannot be created from a snapshot.
o Data is recorded in the history log in UTC (Coordinated Universal Time).
o Restore points in the console are displayed according to the system time zone of the computer running the console.
o The timestamp in the default rollback name is the creation time displayed in UTC (Coordinated Universal Time).
To create a rollback:
1 In the Virtual Disk Details page>Rollbacks tab, click the link Create rollback to open the Create Rollback dialog box. (This operation can also be initiated from the Ribbon or via the context menu from the panels and any virtual disk list.)
2 In the dialog box, a default name is provided for the rollback. The default consists of the name of the source virtual disk and timestamp. Replace the name and enter a description if desired.
3 Select the Restore Point.
· The slide bar represents the history log time period. When you move the slide bar, the time is reflected in the Restore Point field.
· In the Restore Point field, the time can be changed by selecting or entering the date and time.
4 The rollback can only exist on one server, usually the server with the history log. If a rollback is being created on a virtual disk group consisting of virtual disks from more than one server and different members have CDP enabled, select the DataCore Server where the rollback should be created.
5 Choose the rollback
type, which determines the action to take for this rollback in the event that the
history log advances
past the restore point.
This
setting cannot be changed after the rollback is created.
· Select Expire rollback to allow the rollback to automatically expire as the restore point reaches the end of the history log. The rollback will expire without warning and be permanently unusable; it should then be deleted.
· Select Persistent rollback to keep the rollback accessible until the rollback is manually deleted or split. Keeping a rollback persistent can have ramifications. In order to keep the rollback accessible, when the restore point reaches the end of the history log it will not be destaged, therefore, a mirrored virtual disk will have compromised mirror redundancy and a single virtual disk will become inaccessible. In this case, the rollback will have to be manually deleted or split to resume writes to the CDP-enabled virtual disk on the server with the history log.
6 In Storage Profile, select the storage profile of the rollback. (The default setting is Normal, which may be different from the CDP-enabled virtual disk. See Storage Profiles for more information.)
7 Only select the Duplicate disk identifier check box if both source virtual disk and rollback will be served to hosts requiring the same SCSI inquiry ID (virtual product information). For instance, this is required for ESX clusters.
8 Select the Assign ownership to me check box to assign exclusive ownership to the user account currently logged in and creating the rollback. This restricts all operations on the rollback to only the account logged in and the Administrator account.
9 In the pool list, select the pool to use to create the rollback.
10 Click Create.
If unsure
of the accurate point-in-time to select, create several rollbacks with
various restore points. Then serve the rollbacks to the host and determine
the best rollback to use to either revert
the data to an acceptable state or
split the rollback to a fully usable virtual
disk.
After creating a rollback:
o You can monitor the status in the Virtual Disk Details page>Rollbacks tab. Current history log retention period and history log allocated space for the source virtual disk is provided in the Virtual Disk Details page>Info tab.
o The rollback is listed in DataCore Servers Panel under Virtual Disks and in the Virtual Disks List. (The rollback will appear under the selected server.)
o A Rollback Details page is created for the rollback.
Resynchronizes the CDP-enabled virtual disk and the selected rollback, so that the CDP-enabled virtual disk becomes an image of the current state of the rollback, including any changes made to the rollback.
Before
this command is performed, I/O should be stopped and the CDP-enabled virtual
disk should be unserved from the host. This command causes a full
copy from the rollback to the CDP-enabled virtual disk. Reverting will
overwrite all changes that have
occurred on the CDP-enabled virtual disk after
the restore point.
The revert command cannot be performed on a CDP-enabled virtual disk that is:
o Served to a host
Before this command is performed, I/O operations should be stopped and
the virtual disk should be unserved
from the host.
o Mirrored; the mirrored virtual disk must be split first.
o The source of a snapshot; snapshots must be deleted or split first.
o The source of a replication; replications must be split first.
To revert from the rollback:
1 Prepare the CDP-enabled virtual disk to be reverted:
a Stop I/O operations from the host and unserve the CDP-enabled virtual disk.
b Split mirrored virtual disks, delete replications, delete snapshots.
2 In the Virtual Disk Details page>Rollbacks tab, right-click on the rollback with the restore point to which you want to revert and select Revert from Rollback.
3 Click Yes on the confirmation message.
4 After the revert operation is complete, serve the CDP-enabled virtual disk to the host again and resume I/O operations.
5 Delete all rollbacks created from the CDP-enabled virtual disk.
Terminates the relationship between the CDP-enabled virtual disk and the rollback virtual disk. The data on the rollback is preserved. After the operation is complete, the rollback virtual disk becomes a fully usable single virtual disk and is no longer designated as a rollback virtual disk.
When a rollback group is split, a new virtual disk group will be created and the resulting virtual disks will be added to the new group.
Use caution when a virtual disk is using duplicate disk IDs and
is involved with CDP. If the rollback is split, both virtual disks will
have the same SCSI device ID. Under these circumstances, the SCSI device
ID for one virtual disk may need to be changed in order to make it unique.
See SCSI
Standard Inquiry Data.
To split the rollback:
1 In the Virtual Disk Details page>Rollbacks tab, right-click on the rollback that you want to use to recover data and select Split Rollback.
2 Click Yes
on the confirmation message. After the split operation is complete, the
rollback becomes a fully usable virtual disk.
The virtual disk is no longer enabled
for CDP, so enable the option if required.
3 Delete all rollbacks created from the original CDP-enabled virtual disk.
Every CDP-enabled virtual disk has a log that contains the history of data changes. The history log is contained in a designated disk pool on a specified DataCore Server.
The location (DataCore Server and/or disk pool) of the history log is set at the time that CDP is enabled. In order to change the location on virtual disks that have CDP enabled, the feature must be disabled first. and then re-enabled after the location has been changed.
Notes:
o When CDP is disabled, data in the history log will be discarded and rollbacks created from the virtual disk will be deleted.
o Depending on the amount of data in the history log, disabling CDP can take a considerable amount of time. During this process, CDP settings are unavailable. The new server and disk pool cannot be selected until the process is complete. There will be a wait between disabling CDP and re-enabling it.
To change the location of the history log of a virtual disk with CDP enabled:
1 In the Virtual Disk Details page>Settings tab, click Advanced Options.
2 Clear the Continuous Data Protection Enabled check box and click Apply.
3 A warning will appear that disabling Continuous Data Protection can take a long time. Click YES to continue.
4 Wait until CDP has
been completed disabled. This can take a considerable amount of time.
Progress can be monitored in the Virtual Disk Details page>Info
tab.
5 When CDP is completely disabled, in the Settings tab, select the Continuous Data Protection Enabled check box.
6 The history log settings will become available:
a In DataCore Server, select the DataCore Server where the history log should be created.
b In Disk Pool, select the disk pool where the history log should be created.
c In Maximum history log size, enter the maximum log size. When the maximum size of the history log is encroached, the oldest data changes in the history log will be destaged to make room for new data changes.
7 Click Apply.
The maximum size of the history log for the CDP-enabled virtual disk can be changed, but cannot be smaller than the currently allocated size as displayed in the Virtual Disk Details page>Info tab (see History log).
Use caution when decreasing
the maximum history log size of the CDP-enabled virtual disk. The retention
period for a virtual disk is defined by the licensed retention time and
maximum history log size for the source virtual disk. The amount of write
I/Os for the virtual disk will determine how fast the history log will
reach maximum size. The retention period for the history log is provided
in the Virtual Disk Details>Info
Tab (see Retention period).
Since the history
log retention period will fluctuate based on the amount of I/Os written
to the virtual disk, the retention period should only be used as a guideline.
To change the maximum size of the history log:
1 In the Virtual Disk Details page>Settings tab, click Advanced Options.
2 In the Continuous Data Protection area, change the size in the Maximum history log size field.
3 Click Apply.
To delete a rollback:
1 In the Virtual Disk Details page>Rollbacks tab, right-click the rollback and select Delete.
2 A confirmation message appears; read the message. To continue with the operation, click the check box, then click Yes.
