Application Note
Remote Data Migration for iSR6200
Products Affected
QLogic Storage Router
iSR6240
iSR6250
iSR6260
1
Introduction
This application note provides instructions for performing remote data migration using the QLogic
iSR6200 Series of intelligent Storage Routers listed in the Products Affected table. These routers are
collectively referred to as the iSR6200 throughout this application note. The iSR6200 command line
interface is referred to as the CLI, and the SANsurfer® Router Manager utility is referred to as the GUI
throughout this document.
Remote data migration jobs are run as asynchronous mirror operations. During the initial copying
phase of remote online migration, the iSR6200 tracks I/Os occurring in the already copied blocks by
creating dirty region logs (DRLs). Remote online migration also keeps track of the I/Os after the initial
copying phase and creates DRLs. The DRLs are stored in the data management LUN (DML). After the
initial copying phase is complete, the DRLs are flushed continually.
2
Prerequisites
Before configuring remote data online migration jobs, you must configure the DML on the iSR6200. If
you choose to migrate to a remote array in the offline mode, you need not create a DML. DMLs created on
one blade are available for remote migration jobs across both blades. You can configure up to eight LUNs
as DMLs. The maximum supported DML capacity is 2TB. For more information, see the Data Migration
Service for iSR6200 User’s Guide.
3
Remote Migration Use Cases
details on setting up the iSR6200 for these use cases:
Use Case 1: The source array is at the local site, and the destination array is at a remote site.
Use Case 1 typically applies to scenarios where the servers in a data center at Site A (the local site)
are moved to a data center at Site B (the remote site) and the data storage associated with the servers
are consolidated with existing or new storage arrays at Site B.
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4 – Configuration
4.2
Configuring Local and Remote iSR6200 Routers for iSCSI Presentation
To configure local and remote iSR6200 routers for iSCSI presentation, follow these steps:
1. Identify the destination array ports to use for remote migration.
2. Zone the destination array controller ports with remote iSR6200 Fibre Channel ports.
3. Register the remote iSR6200 Fibre Channel ports and provide access to the LUNs on the destination
array.
4. Rescan the targets on the remote iSR6200 to discover the LUNs that were mapped to iSR6200 Fibre
Channel ports on the array.
NOTE:
Some arrays do not allow an iSR6200 Fibre Channel port to port log in (PLOGI) to its Fibre Channel
ports if there are no LUNs mapped to the Fibre Channel port that is logging in. You must generate a
registered state change notification (RSCN) to iSR6200 Fibre Channel ports by disabling and then
re-enabling all connected Fibre Channel ports on iSR6200 blades.
5. Ensure that the destination LUNs are mapped to the remote iSR6200 by issuing the show luns
command on the CLI, or by selecting the FC Discovered Targets or the iSCSI Discovered Targets node
in the GUI’s router tree to see the LUNs.
6. Configure the IP addresses, gateway, and subnet mask in the iSCSI interface(s) on the remote
iSR6200.
7. Configure the iSCSI interface(s) on the local iSR6200 as follows:
a. Configure the IP addresses, gateway, and subnet mask.
b. Set the iSCSI maximum first burst to 64K.
c. Configure the TCP window size for the round-trip time (RTT) and bandwidth to the remote iSR6200.
8. On the local iSR6200, issue the iscsi discover command in the CLI, or use the Discover iSCSI
Target Wizard in the GUI to discover the remote iSR6200 iSCSI port IP address.
9. Verify that the remote iSR6200 shows the local iSR6200 router’s iSCSI qualified name (IQN) by issuing
the show initiators iSCSI command in the CLI, or by viewing the Discovered iSCSI Initiator node
in the GUI.
10. Provide the destination LUN access to the local iSR6200 by following one of these options:
Disable LUN masking on the remote router using the set system command in the CLI (a reboot
of the remote iSR6200 blades is required).
Mask LUNs using the Target Presentation/LUN Mapping Wizard (on both blades) of the remote
iSR6200, presenting the destination LUNs to the local iSR6200 iSCSI initiator IQN.
11.On the local iSR6200, log in to the remote iSR6200 iSCSI targets by issuing the iscsi login
command in the CLI, or by selecting the targets in the iSCSI Discovered Targets node on the router tree
in the GUI.
12.Repeat the login using multiple local and remote iSR6200 iSCSI ports to enable multipathing between
the local and remote iSR6200s.
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5 – Best Practices
13.After successfully logging in, you see the LUNs on the logged-in target as follows:
For Use Case 1, a new array object is formed. Issue the set array command to set the array
type and license the array if required.
For Use Case 2, the discovered iSCSI target paths appear on the previously existing array with
Fibre Channel paths. The Fibre Channel paths are offline, and the iSCSI paths are online. The local
router can now access the LUNs through the iSCSI paths.
4.3
Discovering Remote Devices Through FCIP
The iSR6200 also provides an FCIP feature to discover remote devices. You can use one iSR6200 on
each site to create FCIP links and an additional router for migration. After Fibre Channel switches are
linked using FCIP, the remote Fibre Channel devices are available, just like any other Fibre Channel
device. The iSR6200 used for migration cannot differentiate between a remote or local Fibre Channel
device.
5
Best Practices
For more information on general data migration best practices, see the Data Migration Service for
iSR6200 User’s Guide. The following guidelines describe the best practices:
Start online remote migration jobs during off-peak hours.
If the destination LUN is a thin-provisioned LUN, do the following:
Create new LUNs on the destination site.
In the GUI’s Data Migration Jobs Options dialog box, select the TP Setting option of “Yes without TP
Validation,” which does not copy zero blocks.
When using two iSR6200 routers (one at a local site and one at a remote site), set the migration I/O
size to 64kB. This setting accelerates writes by reducing the latencies involved with the write
command.
Use the bandwidth-limiting feature on the source array to throttle the migration, which in turn limits the
WAN link use.
When using two iSR6200 routers, issue the set iscsi command to manage the RTT and available
bandwidth. Tuning TCP window size based on the RTT is critical to enhanced migration performance.
You can calculate the typical window size in kB as follows:
WAN link bandwidth in MBps RTT in ms
Number of iSCSI connections between the iSR6200 and iSCSI target port of the storage array
For example, suppose the available WAN link bandwidth is 100MBps (1000Mbps), the RTT is 20ms,
and there are two iSCSI connections between the iSR6200 blade and the iSCSI target ports on the
storage array:
100 20 = 1000kB TCP window size
2
Configure a 1MB window size on the iSR6200 and iSCSI target port. The iSR6200 supports a
maximum TCP window size of 16MB. An iSCSI target array port may support larger TCP window sizes.
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5 – Best Practices
Refer to the attached Timeline for Remote Migration Project.xlsx spreadsheet to
estimate the amount of data that can be transferred weekly based on the available bandwidth and
change rate at the source.
NOTE:
The Timeline for Remote Migration Project.xlsx file is a Microsoft® Excel®
spreadsheet that is attached to this PDF.
Remote migration projects depend on the available bandwidth, RTT, and change rate for data under
migration. This spreadsheet provides an estimate of how much data can be migrated online remotely
per week, using the available WAN bandwidth and specified change rate. It also indicates a timetable
on when to start migrations. This method assumes that the application cut-over to the destination starts
on Day 6 and Day 7 of the week.
In the spreadsheet, you must enter the following highlighted values:
Dedicated Bandwidth (Mbps) (the bandwidth of the WAN link used to connect the source and
destination in Mbps).
Change Rate for Data Under Migration (%) (the rate at which the source LUN changes).
The calculation is:
((B4/10%)36002485%)/1000
where:
B4 is equal to the dedicated bandwidth of the configuration (whatever is available).
10% is the change of rate for data under migration.
3600 is the number of seconds in an hour (60 seconds per minute 60 minutes per hour).
24 is the number of hours per day.
85% is the percentage of bandwidth efficiency.
Dividing by 1000 gives a result in GB.
The result is the weekly total GB migrated.
migration on Day 2, and so on. Assuming that the 500Mbps bandwidth entered is available, the cut-over
to the destination is possible on Day 6 or Day 7.
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6 – Remote Migration Topology Examples
6.1
Fibre Channel-to-Fibre Channel Remote Online and Offline Migration
Using iSCSI Presented Targets
remote migration. For offline migration, the servers accessing the source LUN must be shut down and do
not require a DML.
Figure 6-1. Fibre Channel-to-Fibre Channel Remote Online and Offline Migration Using iSCSI
Presented Targets
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6 – Remote Migration Topology Examples
6.2
Fibre Channel-to-Fibre Channel Remote Online and Offline Migration
Using FCIP
remote migration. For offline migration, the servers accessing the source LUN must be shut down and do
not require a DML.
Figure 6-2. Fibre Channel-to-Fibre Channel Remote Online and Offline Migration Using FCIP
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6 – Remote Migration Topology Examples
6.3
Fibre Channel-to-iSCSI Remote Online and Offline Migration
migration. For offline migration, the servers accessing the source LUN must be shut down and do not
require a DML.
Figure 6-3. Fibre Channel-to-iSCSI Remote Online and Offline Migration
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6 – Remote Migration Topology Examples
6.4
iSCSI-to-Fibre Channel Remote Offline Migration
The iSCSI-to-Fibre Channel topology shown in Figure 6-4 supports only offline migration. The iSR6200
does not currently support online data migration when the source LUN is from an iSCSI target.
Figure 6-4. iSCSI-to-Fibre Channel Remote Offline Migration
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Document Revision History
Revision A, November 14, 2011
Revision B, December 6, 2011
Changes
Made minor edits to improve readability.
Modified and attached the bandwidth calculation spreadsheet, and updated the Figure 5-1 screen shot of the
spreadsheet.
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