The role of Tape in Primary Storage Data Protection

Recently I discussed how primary storage, thanks to the use of replication and snapshots, can take a larger role in the data protection and application recovery process. We call this the “Primary Storage Data Protection Strategy”. But, to be effective, this strategy requires three storage systems: two locally and (at least) one remote system in a Disaster Recovery site. Thanks to software-defined storage and the commoditization of storage hardware, an increasing number of companies can now afford this protection strategy. But no company should consider this a complete data protection strategy.

Snapshots Can’t Last Forever

Most modern storage systems use redirected snapshots instead of copy-on-write snapshots. Redirection adds almost no overhead to the snapshot process and allows for a much higher number of snapshots to be active on a storage system. These types of snapshots are also very space efficient, only consuming capacity as old data is updated. New data also consumes storage space but that consumption would have occurred with or without the snapshot.

The real capacity impact of a snapshot is felt when data under snapshot protection is changed. For the snapshot to be valid the old version of that data has to be maintained. As a result, the more snapshots that a system has active and the longer those snapshots remain so, the more of a storage system’s capacity will have to be allocated to snapshots.

Eventually, the storage manager will want to retire older snapshots to free up capacity. But the question is when and where?

When to Retire a Snapshot

The good news, again thanks to the declining cost of storage, is that snapshots can be held for a much longer period of time than in the past. Considering that the large majority of restores are from the most recent protected copy of data, the actual need for snapshotted data could be less than 24 hours. To be safe, an organization may want to keep 48 hours to a week’s worth of snapshots.

Where To Retire a Snapshot

Once data ages beyond this 48 hour window, speed of restoration becomes less of an issue, replaced by a need for cost effective storage and data integrity. Here tape from companies like FujiFilm becomes a much more viable data protection strategy. We suggest that after a snapshot is taken that it be mounted to a backup application and copied to tape. That tape should then be copied again for off-site data placement. Then, in a few days time, the snapshot can be released and capacity returned to the storage system.

Redundancy is Not a Backup

The IT team at Google believes that data is not backed up until it lands on tape, multiple tapes actually. At the FujiFilm Global IT Executive Summit the Google team described a data protection infrastructure that was similar in design to Storage Switzerland’s Primary Storage Data Protection Strategy. They had similar concerns about counting on primary storage redundancy.

The first concern is that corruption and deletions replicate very well. If the corruption is not caught within the 48 hour window that we suggest above, then data loss can result. Also, in the above design, all the storage devices will typically run the same storage software stack, a process that can lead to the same latent bugs in the code.

While the chances of everything going wrong at once are very slim, the consequences if they do are great enough that another layer of protection is needed. We think tape is ideal for this role. It is cost effective so multiple copies can be made and consumes no power and almost no space while at rest. Tape is also a different form of media all together, providing a measure of protection in its diversity.

Finally, reliability of tape is actually higher than that of disk, as long as it’s not damaged in transport. As we will discuss in our next column, transport issues can be addressed by creating a touch-less tape environment, something that the Primary Storage Data Protection Strategy enables quite nicely.


The Primary Storage Data Protection Strategy combined with a solid secondary device like tape can provide robust data protection, meeting both short-term data protection objectives and long-term data retention needs. The two compliment each other quite well and make data protection a more simple, more reliable and more cost effective task than ever before.

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Twelve years ago George Crump founded Storage Switzerland with one simple goal; to educate IT professionals about all aspects of data center storage. He is the primary contributor to Storage Switzerland and is a heavily sought after public speaker. With over 25 years of experience designing storage solutions for data centers across the US, he has seen the birth of such technologies as RAID, NAS and SAN, Virtualization, Cloud and Enterprise Flash. Prior to founding Storage Switzerland he was CTO at one of the nation's largest storage integrators where he was in charge of technology testing, integration and product selection.

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One comment on “The role of Tape in Primary Storage Data Protection
  1. Tim Wessels says:

    Well, assuming you are using current LTO series tape drives for backup why not make sure that you use LTFS formatted tapes, which will help in recovering data from the tape. Two things about tape have troubled me over the years. One problem is the tape drive obsolescence factor and the other is tape sofware vendor support over time. Until IBM, HP and Seagate created the LTO drive and tape format you were basically dealing with individual tape drive hardware vendors. There was some wide spread support for successive generations 4mmDAT and 1/4-inch cartridge formats. But 8mm AIT was Sony-only and the other 8mm formats were almost always vendor specific. LTO was a challenge to the lock DEC then Quantum had on the high capacity DLT/SDLT drive and tape formats. Eventually Quantum acquired Seagate’s tape drive business and LTO became the default choice in the SMB tape backup market. But even with LTO, which is now up to the LTO-6 generation, you can only go back several LTO generations for read compatibility with older LTO media. This means you have to either maintain old LTO drives in “mothballs” or keep transferring older LTO tapes to newer LTO tape formats that can be read by current generation LTO drives. The list of tape sofware vendors has slimmed down substantially due to M&A activity over the years but even when using tape software from the surviving companies you need to keep updating your software version with patches and then upgrade to newer versions as the vendor withdraws support for older versions. All of this should make the case for using LTFS formatted tapes on the LTO tape drives which support it, which I believe are the LTO-5 and LTO-6 series tape drives. Doing this will give you a better chance of getting your data off the tape if you should ever need it.

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