Media Mirror 1.0
The Media Mirror program has three components: Media Mirror, Media Copy, and Media Compare. Media Mirror is the central program, and it manages the mirrors you create between tape drives (Screen 2 shows the mirror between two tape drives in the Media Mirror properties window). Media Copy copies the contents of one tape drive to a second tape drive while preserving the data on the first drive. Media Compare compares two or more mirrored tape drives to confirm that their contents are identical.
I installed the Media Mirror program easily with the installation CD-ROM. You can't install Media Mirror across a network but must perform the installation process at each tape-device server. Media Mirror's product documentation states that the tape drives, media, and adapters you intend to use with Media Mirror must be identical, regardless of whether you use a single or multiple SCSI bus. (Identical means that all matching components in a mirror must be the same make and model.) If you already have heterogeneous tape devices in place, you must invest in identical equipment before you can use Media Mirror.
The most important step in the installation process is creating a mirror between two or more tape drives. For my tests, I used HP SureStore DAT24 units. The Media Mirror setup program automatically detected the HP units, and I easily created a mirror between them by selecting the mirror-creation option during the installation. The program took a short time to create the mirror, then it prompted me to reboot the system. Creating a mirror after the Media Mirror installation process completes is equally easy: I opened the File menu and selected the New Mirror command. An easy-to-follow wizard walked me through the steps of choosing the drives I wanted to mirror, and in less than a minute my new mirror was set up. (Note that you can include each drive you want to mirror in only one mirror.)
When you run a backup with Media Mirror, the media you use must either be blank or contain identical data. The first time I tried to back up with Media Mirror, my media did not contain identical data. The program prompted me to run either the Media Copy utility (to replicate the data on the master tape, which you designate, to all other tapes in the mirror) or the Quick Erase utility (to erase all the data on the mirror's media).
HighGround Systems has approved the use of Seagate's Backup Exec, BEI's Ultrabac, and Microsoft's Windows NT Backup for use with Media Mirror, although the company says Media Mirror should work with any Win32-compliant backup and recovery application.
After I ran Media Mirror successfully with Backup Exec and NT Backup, I wanted to test the effects of using backup software that isn't on HighGround Systems' recommended list. For that purpose I chose Stac's Replica, a program that replicates data from one tape drive to another and that displays the data-transfer rate. Media Mirror ran efficiently during Replica's backup and recovery phases, and I could easily track the simultaneous data writing. I turned off one of the two mirrored tape drives about 20 minutes into Replica's backup process, and the other drive continued unimpeded.
Backups slow when you mirror data because you must add multiple tape devices to one SCSI bus. To optimize speed when you use Media Mirror, HighGround Systems recommends that you install each tape drive on its own SCSI bus. For my test, I installed two tape drives on one SCSI bus, and my backup rate was about 25 percent slower when I used Media Mirror than it is when I back up with one tape drive. Dropping from a backup speed of 60MB per minute to 45MB per minute might not affect small companies negatively, but this reduction can have a major effect in a large enterprise.
Media Mirror lets you use the virtual drive (or mirror) in recovery procedures. When you use the same recovery procedures your backup software recommends in conjunction with Media Mirror's virtual drive, Media Mirror's mirroring capability protects against media or drive failure. In my tests, Media Mirror continued my backup software's recovery process even after I turned the power off for one of the two mirrored tape drives halfway through the recovery.
Media Mirror is easy to use, but it has limitations. The biggest limitation is the hardware requirements--you must use identical tape drives. You can purchase Media Mirror bundled with two Exabyte or two ADIC tape drives, but I'd like to see it handle heterogeneous tape drives, because that would expand this product's possibilities. For now, potential users must decide whether living with an investment in Media Mirror and whatever extra hardware is necessary to use it is easier than living with the potential risks inherent in single-device backups.
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