These days, most data backup administrators are faced with the task of backing up a data set that is expanding
exponentially within a backup window that isn't. Although continuous data protection (CDP) solutions can help with this problem to some degree, the data must still eventually be written to tape for long-term storage. As such, upgrading from LTO-3 tape drives to higher capacity LTO-4 tape drives is a tempting solution. Although an upgrade is usually worth the effort, there are some issues that you need to take into account as you make the transition.
The advantages of upgrading to LTO-4
The LTO-4 standard offers some very compelling reasons for upgrading. The 400 GB native tape capacity found in the LTO-3 standard has been doubled to 800 GB. The maximum transfer speed has also been increased from 80 MBps to 120 MBps. An added benefit is the fact that the LTO-4 standard allows for 256-bit AES-GCM drive level encryption.
Backward compatibility: LTO-4 and LTO-3
The most important issue that you need to take into account when upgrading to LTO-4 tape drives is backward compatibility with your previous tapes. After all, you don't want to find yourself in a situation in which you can't restore the data that was backed up a week prior to the upgrade.
The LTO-4 standard requires LTO-4 tape drives to be fully backward compatible with LTO-3 tapes. LTO-4 tape drives are also designed to be able to read (but not write to) LTO-2 tapes.
I would strongly recommend testing your LTO-4 tape drive's ability to read your legacy backup tapes. Although the standard requires LTO-4 drives to be backward compatible, not every manufacturer follows the standard's exact specification. It is also possible that your backup software may not allow you to read your legacy tapes in your new tape drive. More than likely you won't have any backward compatibility issues, but if any issues do exist you need to find out about them up front rather than down the road when you need to perform a critical restoration.
Although not as critical as the backward compatibility issue, another consideration that you need to take into account is whether or not your servers can deliver enough throughput to take full advantage of the LTO-4 drive. LTO-4 drives are designed to be 50% faster than LTO-3 drives (120 MBps as opposed to 80 MBps). You can still benefit from the LTO-4 drive's increased capacity even if your servers aren't fast enough to take advantage of the drive's increased maximum throughput. The problem is though, that if you increase the tape capacity without increasing throughput, then you may run the risk of exceeding your backup window as the volume of data that you are backing up each night increases.
Proprietary tape formats
Another issue to watch out for is that of proprietary tape formats. Most manufacturers offer the ability to compress the data that is being written to the tape. Over the years, I have seen a few examples of manufacturers who use non-standard tape formats in the interest of providing a higher rate of compression than their competitors. These non-standard formats are fine for the time being, but eventually the day will come when the LTO-4 standard is outdated, and you may be replacing your LTO-4 drive with a next generation LTO-5 tape drive. The LTO Consortium will be offering LTO-5 tape technology, which is scheduled for release sometime in early 2010. When that day comes, you may find that your LTO-5 drive can't read your LTO-4 tapes if they use non-standard compression. In other words, if you buy a tape drive that uses some kind of exotic hardware-level compression instead of using the industry standards, then when it comes time to upgrade, your future tape drives may not be able to read the tapes that you are creating today. If you are going to use compression, then it is best to stick to the norm.
Tape encryption and LTO-4
A similar concern exists with the LTO-4 drive's native compression feature. The encryption feature has been the driving force behind many organizations adopting the LTO-4 standard. Even so, adding encryption to the mix adds the potential for data loss due to lost encryption keys.
Before you implement LTO-4 native compression, you must ensure that you have a good key management solution in place. Remember that your backups are supposed to be able to save you from a worst case failure situation. If the catastrophe that leads to the need to restore your data also causes your encryption keys to be wiped out, then you may be out of luck.
Does your existing backup software support LTO-4?
One last concern that you need to take into account is whether or not your backup software supports LTO-4 drives. The LTO-4 standard has been around since 2007, so pretty much any backup software that was released in the last year or two should support LTO-4. If you are using an older backup application though, you may need to upgrade to a newer release. In addition, LTO-4 tapes are slightly more expensive than LTO-3 tapes.
For the most part, your transition from LTO-3 to LTO-4 tapes should be fairly painless. Even so, it is absolutely critical that you test your new backup solution for reliability and backward compatibility.
About the author:
Brien M. Posey, MCSE, has previously received Microsoft's MVP award for Exchange Server, Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. You can visit Brien's personal website at www.brienposey.com.
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