The numbers don\u2019t look good\nMy favorite source of numbers for the tape industry used to be the Santa Clara Consulting Group.\u00a0 They\u2019d been tracking the use of tape in the backup and recovery industry since 2008 and had been a great go-to for such data. They showed a steady decline in number of units shipped, both in terms of drives and media.\u00a0 Unfortunately, it looks like they stopped doing these services in 2014.\nGartner\u2019s most recent report on what media types people are using to do their backups is a pretty solid source of data, though. They\u2019ve got data going back to 2009 that shows the percentage of people that are backing up directly to tape (D2T), backing up to disk then copying to tape (D2D2T), backing up to disk with no tape component (D2D\/D2D2D), or backing up to the cloud (D2C\/D2D2C).\u00a0 While tape is used in most datacenters in one way or another, the percentage of companies using tape in any way is steadily declining. Companies are clearly moving to D2D or D2C techniques.\u00a0 What are the reasons behind this trend?\nTape is not unreliable \u2013\u00a0it\u2019s incompatible\nSome would say the reason that most people have moved to a D2D2T methodology is that disk is more reliable than tape. I believe the previously mentioned trend shows just the opposite; most people still trust tape as their ultimate line of defense.\u00a0 In fact, some vendors that started out pushing a \u201cno-tapes\u201d message were eventually forced to come up with a method to copy to tape. I do believe this was primarily driven by cost, but even so.\u00a0 Customers don\u2019t push for something they don\u2019t trust -- even if it\u2019s cheaper.\u00a0 D2D2D and D2D2C have been viable options for years now.\u00a0 If customers didn\u2019t trust tape, they would have all moved off it regardless of cost. But believe that it\u2019s still the least expensive way to get the job done \u2013 and so they stay.0\nI\u2019ve been saying for many years that tape is more reliable than most people give it credit for. The problem with tape is its fundamental incompatibility with how backups are done today. Let me explain. Back when dinosaurs roamed the earth and I was cutting my teeth on backups, it was very common to do daily full backups. If you had network issues, you might scale that back to weekly full backups.\nBut today\u2019s backup systems perform full backups much less frequently. They might do them once a month, and they might not do them at all.\u00a0 The thinking is that the logistics of tracking all those tapes are much easier than the old days, so we can afford to do full backups less frequently. In addition, this saves money in media and network usage.\u00a0 The result is that 96% or more of today\u2019s backups are incremental backups \u2013\u00a0and incremental backups are fundamentally incompatible with modern tape drives.\nWith a few exceptions, modern tape drives are linear style drives. This means that they store data in multiple parallel streams as the tape is pulled past a stationary write head, like the cassette tape drives of old. The tape is being moved extremely fast across these write heads, and it must do so to maintain a good signal-to-noise ratio.\u00a0 Due to this requirement, each drive type has a minimum transfer speed at which it can safely write data to tape.\u00a0 For example, the slowest an LTO-6 drive can write data is 40 MB\/s before compression, which means 60-100 MB\/s once you add compression. Rarely will an incremental backup generate anywhere near 60-100 MB\/s. Instead, they can trickle along at a few MB\/s depending on a variety of factors.\nWhat happens is the drive spins up to its minimum speed and transfers the data from the drive\u2019s cache onto tape.\u00a0 If the incoming data rate is slower than the drive\u2019s minimum speed, the buffer will be empty when the drive looks at it again for more data.\u00a0 The drive will need to stop, reposition the write head back to before it stopped writing data, then wait for the buffer to be full again.\u00a0 Once it\u2019s full, the process starts all over again. This process of swiping the tape back and forth across the write head is referred to as shoe-shining, and it prematurely wears out the media, the write head, and the mechanics of the drive. And yes, if you shoe-shine too much, you can make a reliable drive unreliable.\u00a0 This is why I say tape drives are fundamentally incompatible with the way people do backups today.\nNo problem, say backup vendors! We\u2019ll just interleave\/multiplex a bunch of backups together to make the tape drive happy!\u00a0 That might make the backup better, but it will make the restore slower.\u00a0 This is because you need to read all the multiplexed streams and throw away the ones you don\u2019t want.\nDisk and cloud also offer so much more\nThe incompatibility of tape made IT personnel start looking. But the true reasons behind IT\u2019s move away from tape were the things that disk, and cloud made possible. These reasons start with deduplication. Yes, it is what made disk closer to (and sometimes less than) the price of tape. But deduplication isn\u2019t possible without disk, so it\u2019s sort of a chicken and egg thing.\nDeduplication also enabled another great feature of disk -- replication.\u00a0 Where tape requires a human to get it to another location, deduplicated backups can easily be replicated to anywhere in the world. Initially this was to another datacenter down the street, but it grew to include replicating to the cloud, or even sending backups directly there.\u00a0 Now we get onsite and offsite backups \u2013\u00a0without physically moving anything or involving any humans in the process.\nVery closely related to deduplication is the idea of having multiple copies of something share the same storage.\u00a0 Think snapshots on a filer, for example.\u00a0 Most of the bits are all the same; only the differences between the snapshots take up extra space. This allows things that simply aren\u2019t possible with tape. Create a test copy and a development of the same data, without taking up much additional space.\nDisk-based backups also allow you to run servers or VMs directly from their backup. Doing that has changed everything. It allows for much faster recoveries, and even recoveries in place. The idea that you could a recovery without a restore has changed so much about backup that it\u2019s hard to even think about a time when it wasn\u2019t possible.\nPutting all these features together: deduplication, replication, linked copies, and recovery directly from the backup, and you see why the cloud makes so much sense as a perfect companion to all these features.\u00a0 You can also see why those who have made this move \u2013 away from tape, towards disk, and eventually to the cloud \u2013 find it hard to look back.\nNot dead, but dying\nTape is still good at holding onto data for really long periods of time and is still cheaper than most anything else.\u00a0 Such long-term storage needs will ensure that tape will continue to have a role to play for many years to come.\u00a0 But even this last bastion of tape is being challenged by customers who are discovering other uses for older data. Once a company figures out how to monetize that data, they\u2019re going to want it on disk.\nAs far as backup and recovery goes, the extreme differences in functionality between tape and disk \u2013 as well as the shrinking difference in cost\u00a0\u2013\u00a0is pushing many people towards disk and the cloud.\u00a0 Disk allows features like deduplication, replication, linked copies, recovery directly from the backup, and recovery of an entire datacenter in the public cloud. The trend started several years ago, and it will continue for some time.