Specifically, this article is about why modern tape drives are a really bad choice to store the initial copy of your backups. It’s been this way for a long time, and I’ve been saying so for at least 10 years, in case anyone thinks I’ve been swayed by my current employer. Tape is good at some things, but receiving the first copy of your backups isn’t one of them. There are also reasons why you don’t want to use them for your offsite copy, and I’ll look at those, too.
Tape drive are too fast for incremental backups
- Tape drives are too fast
- In case you didn’t know it, modern tape drives essentially have two speeds: stop and very fast. Yes, there are variable speed tape drives, but even the slowest speed they run at is still very fast. For example, the slowest an LTO-7 drive can go using LTO-7 media is 79.99 MB/s native. Add compression, and you’re at 100-200 MB/s minimum speed!
- Incremental backups are too slow
- Most backups are incremental backups, and incremental backups are way too slow. A file-level incremental backup supplies a random level of throughput usually measured in single digits of MegaBytes per second. This number is nowhere near 100-200 MB/s.
- The speed mismatch is the problem
- When incoming backups are really slow, and the tape drives want to go very fast, the drive has no choice but to stop, rewind, and start up again. It does this over and over, dragging the tape head back and forth across the read write head in multiple passes. This wears out the tape and the drive, and is the number one reason behind tape drive failures in most companies. Tape drives are simply not the right tool for incoming backups. Disk drives are much better suited to the task.
- What about multiplexing
- Multiplexing is simultaneously interleaving multiple backups together into a single stream in order to create a stream fast enough to keep your tape drive happy. It’s better than nothing, but remember that it helps your backups but hurts your restores. If you interleave ten backups together during backup, you have to read all ten streams during a restore — and throw away nine of them just to get the one stream you want. It literally makes your restore ten times longer. If you don’t care about restore speed, then they’re great!
What about offsite copies?
Their have been many incidents involving tapes lost or exposed by offsite vaulting companies like Iron Mountain. Even Iron Mountain’s CEO once admitted that it happens at a regular enough interval that all tape should be encrypted. I agree with this recommendation — any transported tape ought to be encrypted.
Tape is still the cheapest way to get data offsite if you are using a traditional backup and recovery system. If you’re using such a system, you have to buy an expensive deduplication appliance to make the daily backup small enough to replicate. These can be effective, but they are very costly, and there are a lot of limits to their deduplication abilities — many of which make them cost more to purchase and use. This is why most people are still using tape to get backups offsite.
If you have your nightly backups stored on disk, it should be possible to get those backups copied over to tape. That is assuming that your disk target is able to supply a stream fast enough to keep your tape drives happy, and there aren’t any other bottlenecks in the way. Unfortunately, one or more of those things is often not the case, and your offsite tape copy process becomes as mismatched as your initial backup process.
In other words, tape is often the cheapest way to get backups offsite, but it’s also the riskiest, as tapes are often lost or exposed during transit. Secondly, it can be difficult to configure your backup system properly to be able to create your offsite tape copy in an efficient manner.
I thought you liked tape?
I do like tape. In fact, I’m probably one of the biggest proponents of tape. It has advantages in some areas. You cannot beat the bandwidth of tape, for example. There is no faster way to get petabytes of data from one side of the world to another. Tape is also much better had holding onto data for multiple decades, with a much lower chance of bit rot. But none of these advantages come into play when talking day-to-day operational backups.
I know some of you might think that I’m saying this just because I now work at a cloud-based backup company. I will remind you that I’ve been saying these exact words above at my backup seminars for almost ten years. Tape became a bad place to store your backups the day it started getting faster than the network connection backups were traveling over — and that was a long time ago.
What do you think? Am I being too hard on tape?
----- Signature and Disclaimer -----
Written by W. Curtis Preston (@wcpreston). For those of you unfamiliar with my work, I've specialized in backup & recovery since 1993. I've written the O'Reilly books on backup and have worked with a number of native and commercial tools. I am now Chief Technologist at Druva, the leading provider of cloud-based data protection and data management tools for endpoints, infrastructure, and cloud applications. These posts reflect my own opinion and are not necessarily the opinion of my employer.