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Oracle® ZFS Storage Appliance Administration Guide
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Document Information

Using This Documentation

Chapter 1 Oracle ZFS Storage Appliance Overview

Chapter 2 Status

Chapter 3 Initial Configuration

Chapter 4 Network Configuration

Chapter 5 Storage Configuration

Chapter 6 Storage Area Network Configuration

Chapter 7 User Configuration

Chapter 8 Setting ZFSSA Preferences

Chapter 9 Alert Configuration

Chapter 10 Cluster Configuration

Chapter 11 ZFSSA Services

Chapter 12 Shares, Projects, and Schema

Chapter 13 Replication

Chapter 14 Shadow Migration

Data Migration

Traditional Data Migration

Migration via Synchronization

Migration via External Interposition

Shadow Migration

Shadow migration behavior

Restrictions on Shadow Source

Shadow File System Semantics During Migration

Identity and ACL Migration

Shadow Migration Management

Creating a Shadow Filesystem

Managing Background Migration

Handling Migration Errors

Monitoring Migration Progress

Canceling Migration

Snapshots of Shadow File Systems

Backing Up Shadow File Systems

Replicating Shadow File Systems

Shadow Migration Analytics

Shadow Migration Requests

Shadow Migration Bytes

Shadow migration operations

Migrating Local File Systems

Shadow Migration Tasks

Testing Potential Shadow Migration

Migrating Data from an Active NFS Server

Chapter 15 CLI Scripting

Chapter 16 Maintenance Workflows

Chapter 17 Integration


Monitoring Migration Progress

Monitoring progress of a shadow migration is difficult given the context in which the operation runs. A single filesystem can shadow all or part of a filesystem, or multiple filesystems with nested mountpoints. As such, there is no way to request statistics about the source and have any confidence in them being correct. In addition, even with migration of a single filesystem, the methods used to calculate the available size is not consistent across systems. For example, the remote filesystem may use compression, or it may or not include metadata overhead. For these reasons, it's impossible to display an accurate progress bar for any particular migration.

The ZFSSA provides the following information that is guaranteed to be accurate:

These values are made available in the BUI and CLI through both the standard filesystem properties as well as properties of the shadow migration node (or UI panel). If you know the size of the remote filesystem, you can use this to estimate progress. The size of the data copied consists only of plain file contents that needed to be migrated from the source. Directories, metadata, and extended attributes are not included in this calculation. While the size of the data migrated so far includes only remotely migrated data, resuming background migration may traverse parts of the filesystem that have already been migrated. This can cause it to run fairly quickly while processing these initial directories, and slow down once it reaches portions of the filesystem that have not yet been migrate.

While there is no accurate measurement of progress, the ZFSSA does attempt to make an estimation of remaining data based on the assumption of a relatively uniform directory tree. This estimate can range from fairly accurate to completely worthless depending on the dataset, and is for information purposes only. For example, one could have a relatively shallow filesystem tree but have large amounts of data in a single directory that is visited last. In this scenario, the migration will appear almost complete, and then rapidly drop to a very small percentage as this new tree is discovered. Conversely, if that large directory was processed first, then the estimate may assume that all other directories have a similarly large amount of data, and when it finds them mostly empty the estimate quickly rises from a small percentage to nearly complete. The best way to measure progress is to setup a test migration, let it run to completion, and use that value to estimate progress for filesystem of similar layout and size.