Adding a file replication rule

Replication and Disaster Recovery Administration Guide for Hitachi NAS Platform

Version
15.1.x
Audience
anonymous
Part Number
MK-92HNAS009-29
  1. Navigate to Home > Data Protection > File Replication Rules, and then click add to display the Add Rule page.


  2. Enter the requested information.
    Important: In general, the system default settings for this page are correct for handling most replication policies; however, in specific cases, the default values for some of the fields on this page are set when configuring the Network Data Management Protocol (NDMP). In these cases, the value might be specified by an ndmp-option setting on the server that overrides the system default. The ndmp-option command sets global system default values for certain NDMP options. These options apply to NDMP operations unless they are overridden by explicit settings sent by the NDMP client, including settings in the Replication Rule page.

    When applicable, exceptions to the system defaults are noted in the following table.

    CAUTION:
    Particular caution should be exercised when setting snapshot options (if the intent is to use the replication for incremental copies).
    Field/Item Description Default
    Name Name of replication rule. The rule name is may include only alphanumeric characters, hyphens, and underscores.  
    Description Free-form description of what the replication rule does.  
    Files to Exclude Specifies files or directories to exclude from a replication. When specifying a file or directory, enter either:
    • A full path name, relative to the top-level directory specified in the replication path. The path name must begin with a forward slash (/); at the end, an asterisk (*) can be entered as a wildcard character.
    • A terminal file or directory name, which is simply the last element in the path. The name may not contain a character, but it may start or end with a wildcard character *.
    • A list of files or directories to exclude from a replication. When listing files or directories to exclude from a replication, all items in the list must be separated by a comma.
    None are excluded.
    Block-based Replication Minimum File Size Block replication minimum file size controls the minimum file size that is used for block replication. The list options available are: 256 or 512 K, and 1, 2, 4, 8, 16, 32, 64 or 128 MB. For instance, if this option is set to 64 MB:
    • For a source data file of 63 MB, for which the system determines that only 1 MB has changed, the entire source file (63 MB) will be replicated.
    • For a source data file of 65 MB, for which the system determines that only 1 MB has changed, only the delta will be replicated.
      Note: Requires a Replication license to function.
    Minimum file size used for block replication is 32 MB.
    Use Changed Directory List Indicates if incremental replications will search for changed files in directories that only contain changed files. Processes not using the changed directory list must search the entire directory tree looking for changed files. When using the changed directory list, however, the search only is limited to those directories that contain changed files.
    Options:
    • system default: uses the currently specified system default.
    • Enabled: uses the changed directory list.
    • Disabled: always searches the entire directory tree for changed files (a full hierarchical search).
    Note: Using the change object list is likely to improve performance in some cases; for example, where there are sparse changes. However, it can degrade performance where there are many changes throughout the directory structure.

    The calculation of the change list might take a long time as there can be a long delay between replications. Use Changed Directory List should only be selected if a large part of the directory tree will be unchanged between replication copies. Also, the list can include up to one million directories that contain changed files. If this limit is exceeded the replication reverts to a full hierarchical scan.

    Use Changed Directory List is disabled.
    Number of Additional Server Connections Controls the number of additional server connections that are established during a replication operation. Ranges from 0 to 30. Increasing the number of additional server connections might improve performance by allowing multiple transfers in parallel.
    Note: Each additional server connection consumes system resources, and best practices indicate limiting the number of additional server connections to situations in which they improve performance. Also, as the number of additional server connections is increased, more read-ahead processes are required.
    Number of additional server connections that are established during a replication operation is four.
    Number of Read Ahead Processes Controls the number of read-ahead processes used when reading directory entries during a replication.

    Each additional read-ahead process uses system resources, so it is best to limit the number of additional processes unless it makes a significant difference in performance.

    While the default number of read-ahead processes is suitable for most replications, file systems made up of many small files increase the amount of time spent reading directory entries proportionately. In such cases, adding additional read-ahead processes may speed up the replication operation.

    If a value is not set, the default value is set by the application (depending on the number of read-ahead processes set in Number of Additional Server Connections).
    Pause While Replication(s) Finish Writing By default, the data management engine imposes an interlock to stop NDMP backups and accelerated data copies (ADCs) from the destination of a replication during active replication writes. This function supports installations that replicate to a particular volume, then back up from that volume. However, as the lock is held at the volume level, it may be useful to override this action in the case of directory-level replication.

    To make use of this replication interlock, specify this rule option on both the replication that waits and the replication that is waited upon. As a best practice:

    • Create one rule with this option enabled and have each participating replication policy enable the same rule.
    • Then, schedule the replication policy that waits to run after the replication policy that is waited upon.
    Set to no.
    Take a Snapshot Overrides the Backup configuration option Automatic Snapshot Creation. The setting for this option should be left as the system default in almost all cases. The only case in which it might be useful is when taking a single, non-incremental copy of a file system or a directory. If there is insufficient space on the file system to take a snapshot, the copy may be taken from the live file system by selecting Disable. However, it should be noted that copying the live file system while it is changing may give an inconsistent copy.

    Disabling snapshot usage will affect the ability to run incremental replications. This option should only be set to No if the rule is going to be used for a one-off full replication.

    • Enable this option to support incremental replication copies.
    • Disable only for full replication copies or when making a complete copy of a directory.

    Different files will be copied at different times, so if the source file system is changing and there are dependencies between different files on the system, then inconsistencies may be introduced.

    Note: Snapshots are an integral part of the algorithm for incremental replication, and disabling snapshot usage will affect the ability to run incremental replications. This option must be enabled in order to make incremental replication copies.
    Snapshots are taken and backed up automatically.
    Delete the Snapshot Determines when snapshots are deleted. The setting for this option should be left as the system default in almost all cases. The only case in which it might be useful is when taking a single, non-incremental copy of a file system or directory. If the file system is short on space, it may be useful to request the immediate deletion of the snapshot taken for the replication. The deletion options are:
    • IMMEDIATELY gives the same effect as Delete snapshot after replication is done.
    • LAST preserves snapshot for use with incremental replications.
    • OBSOLETE deletes an automatically created snapshot when the next backup of the same level is taken.
    CAUTION:
    As changing these settings can adversely effect the replication process, customer support recommends that this option be changed only at the direction of your Hitachi Vantara LLC representative.
    If the replication is an incremental replication, the application automatically selects the correct setting.
    Migrated File Exclusion Indicates if the replications will include files whose data has been migrated to secondary storage.
    • Enabled: the replication will not include files whose data has been migrated to another volume using the Data Migrator facility.
    • Disabled: migrated files and their data are replicated as normal files.
    Disabled
    Migrated File Remigration Controls the action at the destination when the source file had been migrated.
    • Enabled: the file will be remigrated on recovery provided the volume or virtual volume has a Data Migrator path to indicate the target volume.
    • Disabled: all the files and their data will be written directly to the recovery or replication destination volume.
    Remigration of the files is attempted.
    External Migration Links Controls when a replication operation encounters a cross volume link (a link to a file that has been migrated to an external server).
    • If set to system default, the replication operation uses the default setting, which is remigrate.
    • If set to remigrate, the replication operation copies the file contents but marks the file as having been externally migrated. The destination remigrates to secondary storage if there is an existing data migration path. This is the default behavior. Use this setting when the replication is between a main site and a disaster recovery site, in which the disaster recovery site includes a similar data migration configuration.
    • If set to ignore, the replication operation copies only the files on the primary (migrated files are not copied). Use this setting when files have been migrated because they are less useful, so they are not replicated in order to save time.
    • If set to re-create link, the replication operation copies only the details of the cross volume link. The cross volume link is recreated on the destination if the relevant external migration data path is in place and the migrated file is accessible. Use this setting when the replication is between storage servers or clusters on the same site, and there is a single external migration target server.
    Note: For externally migrated files, to make sure that the file or link is replicated properly, you should either:
    • Specify that the replication operation should remigrate files and the destination should test before recreating links (using the migration-recreate-links-mode command).
    • Specify that the replication operation should re-create links and the destination should always recreate links (using the migration-recreate-links-mode command).
    Remigrate and re-create link are enabled.
    Ignore File Attribute Changes Specifies that files in which the only change is an attribute change, are not included in a replication. Only enable this option if you are certain that you do not want to replicate files with only attribute changes. Disabled