Tape Not Lowest Priced Storage Technology

Since many years, we heard from tape vendors and some analysts than tape is better than disk drive. What do they say?

Tape is cheaper to acquire than disk, less costly to own and operate than disk
That’s completely wrong because you have to compare Apple to Apple. For sure, a $120 LTO-7 cartridge (6TB native) from FujiFilm or Sony is more than twice the price of a 6TB HDD ($250). But what can you do with just a tape cartridge in your hand? Nothing, it’s just a piece of plastic containing a roll tape. You need at least an LTO drive from HP or IBM costing more than $2,500. It changes completely the comparison. On the contrary, an HDD can be used immediately having media/disks, heads, motors,  with a simple interface to your computer. Of course you can buy more cartridges. But you need to get around 21 tape media to reach an equivalent price of the total package with HDDs. Furthermore, you have to insert manually tape cartridges into your high-priced drive. A contrario, it’s possible to connect the equivalent of 10 HDDs together with an appropriate connection to get immediately 60TB online without any manual intervention. You could say that LTO technology can offer 15TB per media assuming 2.5:1 compression. But it’s also possible to compress data before writing them on disk. Note also that 10TB HDDs are already available. LTO-8 at 16TB native will be the next gen but when?

Tape is more reliable than disk
Vendors claim 30 years for the longevity of LTO-7 but the reality is quite different. The same vendors advise to read all your data on tapes each 3 to 5 years to verify their integrity. And if you are unable to read just one file, what do you do? There is no other way that to go to a laboratory specialized in recovering data at a high price. You can also copy twice all your information on different tapes, once more a costly operation. It’s much more simple to verify the integrity of HDD. Just connect it to a computer. If it appears on your screen, the device is in good shape and it exists a lot of utility software to repair it, not for tape. With disks, you have also the possibility to assemble them into a disk array to be more secure. There was some attempts in the past to design tape arrays but there was no market for them, too complicated, too expansive. Furthermore, LTO needs cleaning cartridges because they are not completely closed like HDDs.

Access time much too low
Transfer time is acceptable (300MB/s, 700MB/s with compression), but here are the access times for LTO-7 using 960m tape according to Oracle/StorageTek:

• Tape load and threat to ready: 11s to 13s
• Average access time (first file): 56s to 59s
• Maximum/average rewind time: from 108s/58s to 113s/62s
• Unload time: 19s to 22s

These times are enormous compared to few milliseconds for HDDs. While LTFS can make a tape appear to behave like a disk, it does not change the fundamentally sequential nature of tape.

We are not concluding that tape is dead but the reality is that this market is decreasing since several years. Tapes now can be justified for huge capacity of cold storage only,  in competition with optical disc technology and big cloud storage providers.

Tape autoloaders are a dying market as they use a small number of slots. It’s a little better with mid-range tape libraries but not really convincing. The real market for LTO is now huge libraries with sophisticated robotics.

We tried to get the prices of high-end configurations among two leaders in this field, small companies Qualstar and Spectra Logic (others vendors of tape automation products are HPE, IBM, Oracle, Overland/Sphere 3D and Quantum.) .

Spectra Logic give us the example of its TFinity ExaScale, not so big with 50 slots and 12 LTO drives prices at $502,410 without the media. Adding $6,000 for 50 cartridges, total is $508,410 for a total compressed capacity of 750TB that you can get for with 125 6TB HDDs for only $31,250 or 16 times less.

The comparison could be in favor of tapes with libraries packing more than thousands of LTO cartridges but we are not really able to prove it.

Qualstar offers configurations with up to 1,000 slots and Spectra Logic with up to 53,460 LTO tapes (802PB compressed) and 144 drives for cold storage.

According to VP global sales Arun Vaishampayan, Qualstar’s XLS series, enterprise class tape libraries, are capable of providing from 3.6PB to 70PB of storage capacity. “The price ranges between $85,000 to $2.4 million depending on the configuration,” he said.

If we consider the highest XLS configuration (11,730 LTO-7 cartridges, 20 drives scaling up to 127, from 435 to over 11,730 tapes (native LTO-7), 20 drives, native data rate of 21.6TB/hour, we conclude that is costs $2.4 million for 70.4PB native or 176.0PB with compression, the equivalent of $13.6/TB, less expensive that the same capacity on HDDs ($20.8/TB).

The problem with Qualstar is that Vaishampayan didn’t precise if the $2.4 million configuration includes the price of LTO-7 cartridges and drives as well as software management.

Conclusion: using very high-end tape libraries, and only these ones, it’s worth to consider the tape technology.