MiraLink 400 - 23 Aug 2006

MiraLink Corporation’s MiraLink 400 is a remote data-mirroring appliance designed to be a part of a business continuation–disaster recovery plan. The appliance is a desktop unit with internal Serial ATA (SATA) disk storage. (Other MiraLink remote data-mirroring products support internal SCSI disk storage or external SCSI arrays.) The MiraLink 400 is designed for use in pairs, and each appliance in the pair has its own network connection.The primary MiraLink 400 unit, called the Source unit, connects to the application server at the local site.The Source unit mirrors data written to it in real time over a standard IP connection to the secondary unit, called the Destination unit, which is connected to a backup server at a remote site.

To the server it’s connected to, a MiraLink unit appears as a disk drive. Units typically connect to the application server through a SCSI interface, but Fibre Channel, iSCSI, and NAS connections are also possible. As a SCSI device, the MiraLink is supported in a variety of Windows and other OS environments. The MiraLink 400 isn’t Microsoft-certified for a Windows or SQL Server environment—it hasn’t been tested to qualify for the Designed for Windows (DFW) logo program. However, MiraLink Corporation supports the appliance in most environments that support SCSI disk storage.

You configure MiraLink volumes by using the Microsoft Management Console (MMC) Disk Management snap-in. You can also use MiraLink 400 storage to mirror an application server’s system and boot disks to maintain a bootable copy of the application server at a remote site.

In Windows environments, data on thedestination unit is not available while thesource unit is actively mirroring to it. InUNIX and Linux environments, MiraLinksupports read-only access to data on thedestination unit during active mirroring.

To configure the MiraLink 400, I used two identically configured Windows Server 2003 systems with Adaptec 29160LP SCSI controllers.To speed up creation of the initial mirror, MiraLink Corporation suggests that you initially set up the units on the same network subnet, then ship the Destination unit to its remote location. Physical setup consisted of connecting each MiraLink 400 to its server with a SCSI cable and cabling each server and each MiraLink appliance to an Ethernet switch. Using Microsoft Internet Explorer (IE) to connect to each MiraLink’s Web-based UI, I configured the appropriate IP addresses.

I tested the MiraLink 400 for use with database applications by installing SQL Server 2005 on both the test Source and Destination servers .I installed an application that relies on SQL Server on a third system, placing the application’s database (both data and log files) on a 20GB volume on the MiraLink 400 Source unit. I caused the application to write more than 100,000 records to its database tables. Using both SQL Server Management Studio and the application’s GUI, I monitored changes to the database. After causing the application to write to the database, I unplugged the network cables from the Source MiraLink 400 and its server, simulating a source application server outage.

To use mirrored data on the Destination unit, you use the Web UI to change the Destination unit’s role to that of a Source unit. To test the mirrored database data, I changed the Destination unit’s role and started up its server. Disk Manager reported the MiraLink 400’s storage as a foreign disk, so I imported it and reactivated the 20GB volume. Using SQL Server Management Studio (SSMS), I attached the application database and reconfigured the application server to use the instance of SQL Server 2005 on the new (originally Destination) server. Using both the application’s GUI and SSMS, I confirmed that the database updates I had generated prior to the simulated failure were present on my backup SQL Server.

The MiraLink 400 worked as advertised. The appliance is remarkably easy to install and use. I wasn’t equipped to perform rigorous SQL Server compatibility testing to demonstrate the MiraLink 400’s utility as a target SCSI storage device or as a 100 percent reliable mirroring appliance. I recommend that the MiraLink 400 be paired both with an application that doesn’t require more I/O capacity than the appliance can handle and a network connection that can keep up with the resulting data stream.