Various companies will spin you their “tape is dead” story, and I’m the first to admit that the use pattern for tapes is evolving, but to anyone who claims that tape has lost its relevance, I’ll argue otherwise.
This is part 1 of a 2 part article, and we’ll cover reasons 1 through 5 here.
1. Tape is cheap
Comparatively tape is still significantly cheaper than disk. In AUD, from end-resellers you can buy individual LTO-4 cartridges (800GB native) for $50. Even at a discount price, in Australia you’ll still pay around $90 to $110 for a 1TB drive (the closest comparison).
2. Tape is offline
If your backup server is using traditional backup to disk and is infected by a destructive virus or trojan, you can lose days, weeks, months or perhaps even years of backups.
No software, no matter how destructive (unless we’re talking Skynet levels of destruction) is going to be able to reach out from your infected computers and destroy media that’s sitting outside of your tape libraries. It’s just not going to happen. There’s a tonne of more likely scenarios that you’d need to worry about first before getting down to this scenario.
3. You can run a tape out of a burning building
Say you’ve bought the “tape is dead” argument, and all your backups are in either on a VTL, a standard array for disk backup, or some multi-cluster centralised storage system (e.g., a RAIN as per Avamar). But you’re a small site comparatively, and so you have to buy the replication system in a future budget.
Then your datacentre catches on fire. Good luck with grabbing your array or cluster of backup servers and running out the building with them. On the other hand, that nearby company that also caught fire but stuck with tape had their administrator snatch last night’s backup tape out of the library and run out of their building.
Sure, the follow up response is that you should have replicated VTLs or replicated arrays or replicated dedupe clusters, etc., but it’s not uncommon to see smaller sites buy into the “tape is dead” solution and not do any replication – planning to get budget for it in say, the second year or deployment, or when that colocation datacentre goes ahead in the “sometime later” timeframe.
4. Tapes have better offline bandwidth
Need to get a considerable amount of data (e.g., hundreds of terabytes, maybe even petabytes) from one location to other? Unless you can stream data across your links at hundreds of megabytes per second (still a while away for any reasonable corporate entity), you’re going to have better luck with sending your data via tapes rather than disks. Lighter and more compact than disks, let alone disk arrays, your capacity per cubic metre is going to be considerably higher with tape than it is with disk.
Think I’m joking? Let’s look at the numbers. Say you’ve got a cubic metre of shipping space available, let’s see which option – tape or disk – gives you the most capacity.
An LTO cartridge is 10.2cm x 10.54cm x 2.15cm. That means in 100cm x 100cm x 100cm, you can fit 9 x 9 x 46 cartridges, which comes to a grand total of 3,726 units of media. Using LTO-5 for our calculations, that’s a native capacity of 5,589 TB per cubic metre. Of course, that’s without squeezing additional media in the remaining space, but I’ll leave that up to people with more math skills than I.
A typical 3.5″ internal form-factor drive (using the 1.5TB Seagate Barracuda drive for comparison) is 10.2cm x 14.7cm x 2.6cm. In a cubic metre, you’ll fit 9 x 6 x 38 disk drives, or 2,052 drives. Using 2TB drives (currently the highest capacity), you’ll get 4,104 TB per cubic metre.
So on the TB per cubic metre front, tape wins by almost 1,500 TB.
Looking at weight – we start to see some big differences here too. The average LTO cartridge (using LTO-4 from IBM as our “average”) is 200 grams. A cubic metre of them will be 745.2 KG. That Seagate Barracuda I quoted before though weighs in at 920 grams – so for a cubic metre of disk drive capacity, you’re looking at 1,887.4 KG. There’s a tonne of difference there!
Tape wins on that sort of high capacity offline data transfer without a doubt.
5. Storage capacity of a tape system is not limited by physical datacentre footprint
If you’ve got a disk array, there’s an absolute limit to how much data you can store in it that (as much as anything) is determined by its physical footprint. If you fill it and need to add more storage, you need to expand its footprint.
Tape? Remove some cartridges, put some more in. Your offline physical footprint will grow of course – but if we’re talking datacentres, we’re talking a real, tangible cost per cubic metre of space. Your tape library of course will occupy a certain amount of space, but its storage capabilities are practically limitless regardless of its size, since all you have to do is pull full media out and replace it with empty media. Offline storage space will usually cost up to an order of magnitude less than datacentre space, so disk arrays just can’t keep up on this front.
Reasons 6 through 10 will be published soon.
