Developers Guide

Offline and online mode explained
40 Data Migration from Dell PS Series or PowerVault MD3 to Dell EMC SC Series Storage using Thin Import | 3041-BP-EM
5 Offline and online mode explained
As mentioned in section 2, both offline and online modes of the import process affect service. If possible, it is
recommended to test the Thin Import process in a non-production environment to establish an accurate
outage timeframe.
Note: Total time required for the import process can vary greatly depending on the array configuration,
available bandwidth, and amount of data transferred.
Offline mode requires both the source and destination volumes to be offline for the duration of the process.
Applications that require these volumes will incur an outage during this time. With ESXi datastores, this
means virtual machines will be unavailable for the duration of the process and can be re-added to the
inventory upon completion.
Online mode requires a temporary outage. Total outage time includes the time needed to complete the
following manual processes:
1. Shut down and remove from inventory all virtual machines on the datastore to be imported (VMware
only).
2. Unmount datastore to be imported (VMware only).
3. Halt I/O and remove the server access policy on the PS Series volume, or remove the MD3 volume
from the existing host.
4. Apply an access policy to allow the SC Series storage access to the volumes (PS Series only).
5. Map the volume to the SC Series host object (MD3 only).
6. Start the Thin Import wizard.
7. Run a rescan on the server to recognize the SC Series volume.
8. Bring the SC Series volume online.
9. Re-add virtual machines to inventory and power on (VMware only).
Note: Manual processes in online mode are detailed in a later section.
In some cases, the total outage time for online mode can be less than established application timeout values,
resulting in no service loss.
Note: In both offline and online modes, high latency or any network interruption during the import process will
cause the data copy to fail and restart from the beginning regardless of the amount of data previously copied.
Note: While the import is in process, the host server could see increased I/O latency to the volume being
imported. During an online Thin Import, read and write I/O received from the server are sent from the SC
Series array to the PS Series or MD3 array to be processed. Read I/O is sent to the PS Series or MD3
volume so that reads to data not yet imported to the SC Series volume can be read successfully. Write I/O is
written to the PS Series or MD3 volumes and the SC Series volumes to keep data consistent until the import
finishes successfully. The added traffic between the SC Series array and the PS Series array during the
online import could add noticeable latency to server I/O.