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I'm unsure if this is the correct community, so feel free to move it if you feel it's in the wrong area.

I'm trying to develop a water-tight/sealed box for a backup flash drive. The idea is to make something that is weatherproof enough so I can keep the box outside or in my basement for years, and if I ever need to retrieve the data, I can cut the box open and retrieve the USB stick. This would need to completely resist water/moisture and withstand temperature changes between say -40 C to 40 C without it breaking down.

Here is the concept I have so far:

  • First layer: Put USB stick into air-tight plastic container. Could be something cheap like a sealable zip-lock bag to protect from:

  • Second layer: fill a small box - not much larger than the stick - with a polymer sealant/caulk that will eventually solidify, fitting the form of the box.

My question is, what is the best material can I use for layer #2?

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  • $\begingroup$ How many years, and will it be continuously exposed to sunlight and weather? A cool, dry basement may compared with a rooftop in an Alabama summer may have very different effects on different materials. $\endgroup$ – wwarriner Feb 16 '16 at 1:48
  • $\begingroup$ @starrise ideally it would be for at least 2 years. I'm looking for something that could withstand a wide range of temperatures as the temp varies quite a bit where I live. It would probably not be exposed to sunlight as I'd keep it in a musty basement or a shed/garage outside. Based on Fred's answer below, I'm guessing silicon would fit this. $\endgroup$ – concealed curry Feb 16 '16 at 2:02
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    $\begingroup$ Bitcoin wallet backup? $\endgroup$ – squigbobble Feb 16 '16 at 10:07
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    $\begingroup$ It is important to place a desiccant pack inside of the first layer (i.e. the zip-lock or vacuum-sealed bag). This will absorb any residual moisture trapped in the bag as well as any moisture which permeates through over the years. You can buy a 25-pack for $9.99 on Amazon. $\endgroup$ – Chris Mueller Feb 16 '16 at 15:06
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    $\begingroup$ Honestly, I'd just put the stick and a desiccant pack in a canning jar. $\endgroup$ – Mark Feb 17 '16 at 3:10
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If you have access to a vacuum pack sealer, a vacuum sealed pack for the fist layer would be better option than a zip lock bag. Whatever you use, a first layer will be needed to protect the contacts of the USB stick.

For your second layer, as I understand it, you are wanting to make an encasing weather proof 'brick' around a sealed USB stick. I would suggest clear silicone.

Being clear you'll be able to see the USB stick inside. Some of the relevant properties of silicone are:

  • Low toxicity
  • Low chemical reactivity
  • Thermally stable in a temperature range of $-100\ ^\rm{o}C$ to $250\ ^\rm{o}C$
  • It repels water & is used to create water tight seals
  • It does not support microbial growth

When you need to retrieve the USB stick the silicone can be easily cut with a sharp knife.

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  • $\begingroup$ Thanks for the detailed answer. After looking around a bit online, would this fit the bill? homedepot.com/p/… $\endgroup$ – concealed curry Feb 16 '16 at 2:05
  • $\begingroup$ Yes, I'd use it. $\endgroup$ – Fred Feb 16 '16 at 2:10
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    $\begingroup$ You should add a silica desiccant pack inside of the vacuum bag to soak up any moisture which manages to permeate through. $\endgroup$ – Chris Mueller Feb 16 '16 at 13:08
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    $\begingroup$ I believe that all silicone caulks and glues support mold growth. Just some of them have biocide mixed in. $\endgroup$ – Agent_L Feb 16 '16 at 13:14
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Others have given you an idea of how to seal the data storage device, but I'd like to make you aware of another issue.

USB sticks (especially cheap ones) aren't designed for data archival. The memory storage mechanism degrades over time from many different causes; entropy, cosmic rays, and radioactive decay come to mind. It is entirely possible that you open up your excellently-designed, sealed box after a few years only to find that the memory is unreadable.

There are a few relatively cheap ways to increase your chances of recovering the data:

  • Buy a high quality flash drive with SLC-based memory
  • Buy multiple flash drives and write the same data to each
  • Buy a high capacity flash drive and write many copies of the same data
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  • $\begingroup$ "Buy multiple flash drives and write the same data to each" - and don't store them all in the same basement! It doesn't matter how good your design for a container is, if you can't find in the pile of rubble after an earthquake destroyed your house ;) $\endgroup$ – alephzero Dec 14 '16 at 1:54
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I'm not sure that silicon caulk is the idea material for this for two reasons. Firstly it is very viscous and forms a skin fairly quickly so it is not that easy to ensure that a big blob of it around something will actually make a very good seal and thick sections take very long time to cure.

Secondly the curing process releases acetic acid which has the potential to corrode the very thing you are trying to protect.

If it was me it would either use something like a preserving jar or get a short length of PVC pipe and bond an end cap on each end if you want it tamper proof or use threaded pipe fittings to do the same thing if you want easy access, just seal he threads with PTFE tape or sealing compound.

Also, whatever solution you go for I would, at the very least add a couple of sachets of desiccant granules to the package to remove any moisture from the air inside, or if you wan to be really thorough you can get oxygen scavenging inserts for archival purposes.

As others have mentioned a flash drive is probably a better choice for archiving than USB.

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  • $\begingroup$ I think a "flash drive" is the same as "USB". Did you mean a "memory card" instead? $\endgroup$ – unfa Sep 28 '18 at 9:16
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1) You should not use a regular USB stick. It simply has too much exposed circuitry inside that can go bad. You should rather use a memory card or a dedicated, weatherproof stick like:

  • Corsair Flash Voyager
  • LaCie RuggedKey
  • Patriot Supersonic Boost XT

2) Rather than trying to create a container around the thumbdrive you should use a case that's already designed to do that. One of best performers are aluminium containers with rubber or silicone seal that is compressed when the box is closed. This compression gives much better performance than using silicone caulk or glue. Quick search revealed they're easily found: Aluminium airtight storage cylinder. I have no experience with this particular product, but it does everything I wrote: 2-piece body with o-ring inbetween.

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I'd like to mention something else that will improve the retention of your data. If you want your data to be really safe - make a few copies. To be safe even if parts of the data are corrupted.

If you have multiple physical copies of your data (say: 3 memory cards holding the same files) you can use a tool like ddrescue to heal problems in one copy with the other one.

This way even if some of the data gets corrupted - you have a very high chance of recovering it all as random errors will most likely not corrupt the same bytes in all of your copies. The more copies you have - the more recoverable your data is.

If you still have some holes in your ddrecovered LZIP archive - you can use lziprecover to fix any residual errors.

Another approach could be to create a ZFS pool on multiple USB drives or memory cards and set them to work in mirror mode. ZFS is a filesystem/volume manager designed to prevent data loss used in data centers and NAS deployments around the world.

You'd need to use Linux or Solaris for that though.

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