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Comment by einpoklum | Hacker News Reader

> LTO Tape is ... much cheaper than hard drives ... a 12TB SATA drive costs around £18.00 per TB ... a LTO-8 tape that has the same capacity costs around £7.40 per TB ... That’s a significant price difference.

Actually, it isn't very significant. Price factor of 2.5. I had thought tape storage was cheaper than that. And then there are the drives: A drive to write (3,000 GBP for LTO-8), and at least a couple more drives for reading tapes.

At this price ratio, I would say that ease-of-use and safety/robustness of the backed-up material are more important considerations.

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What was actually ignored at that comparison is energy costs. Which can get quite somewhere, if you have all your disks running 24/7 and do not use power saving functions (which is frequently turned off in server contexts). Costs are in the ballpark of 5W per drive, given a contemprary 16TB drive this means 0.3W/TB, with 0.25EUR/kWh (a typical consumer price in Germany), this is roughly 0.6 EUR per TB per year. However, probably the replacement costs for these always-on disk drives will be even higher.

Another consideration related to this is that tapes, being usually offline, as much more secured against accidental (or malicious!) erasure when compared to always-on hard drives.

Also related is that tapes can easily be transported around/offsite, literally thrown in the back of a truck as they are. Try doing that to hard drives and see how many start throwing bad sectors after a round-trip.

HDD's can be taken offline. But beyond that - if you're using HDDs as backup, you'll probably be using an HDD drawer, e.g. something like one of these:

https://www.newegg.com/global/p/pl?d=hot+swap+hard+drive+bay

... and the actual disks will usually be stored offline. So, no accidental erasure. But I agree that tapes are probably less sensitive to transportation.

Tapes are offline and even require manual loading, so I think it's feasible to mitigate this by just powering down the backup system. At least that's what I do (with my primary NAS). But yeah, disk idle usage should not be underestimated.

Also, some nit-picking: Energy prices in Germany are currently MUCH higher than that. We moved and had to get a new contract. Close to 40c/kWh. This makes your point a bit stronger.

//edit: Also2, when doing the math I realized I should first transcode suitable content to h265 (per TB saved the necessary power is cheaper than a new disk), and as a second step replace my four or five remaining 1 TB HDDs with a single bigger drive to reduce the idle power draw (the NAS is on a btrfs mixed-size RAID1).

If you want tape-like offline storage on HDDs, you can use a SATA docking station. Keep the 'active' backup drives plugged in, store full drives wherever you like.

As a bonus, they can generally be used to offline clone drives.

I am also worried for the long-term. If there are new generations so frequently and backwards compatibility is limited or not guaranteed, I ponder if you'd be able to find a working-condition tape reader for your 20-year old tape...

At least it's likely I can find a USB port 20 years from now, or a DVD reader (they are still being manufactured today, when even more than 20 years have passed since their introduction, and they are even compatible with much older CDs...).

Yes, this doesn't sound quite right to me but it may be an economies-of-scale thing. I work on an HPC system and we budget an order of magnitude less for tape storage, and that has held for quite a few years.

> and at least a couple more drives for reading tapes.

Why?

If you have 500TB of tape, the chances are that you are reading at least one tape while also needing to write stuff.

I've personally never experienced that scale, I'm sure the industry has some recommended ratio of drives to tapes.

When I evaluated this, it was all about read and write access patterns. So much data coming in for so much amount of time, that needs so much validation, and will be restored so many times in the next few years, etc. It's pretty easy if you know your data flows, but when it's a big question mark, you just kind of throw hardware at it and fix the bottlenecks when they come up. We usually wrote more than we read, but we absolutely needed to keep read capacity open.

Backups are there so that they can be restored. If your only drive is dedicated to writing, then you may never bother reading anything, and that's bad because you should verify your backups.

Also, tape is slow. The MB/s is pretty nice on the latest tech, but a tape is pretty big, so if you have a lot of stuff it'll take a good while. Google says it takes 9.25 hours to write a full LTO8 12TB tape. Which means that if you have a sizable backup, in case of needing a full restore you might well spend a whole week reading tapes.

And that's not accounting for that something might suddenly break, and the time where that becomes important is right when you need something restored urgently.

Even in an "enterprise+++ class" multi petabyte, multi drive, totally integrated from top to bottom tape archive for scientific data, there would be all kinds of errors found by our data validation process that would have failed an archive restore. It's not just cache overruns, some times the tapes or drives just screwed up silently.

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