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Hardware systems like traditional RAID, or modern software systems like ZFS, btrfs, etc. are used for redundancy (and performance) of the storage of data. Whenever a drive dies in one of these redundant systems the process of writing data to it is called resilvering. Where did this phrase come from?

I've looked around for any sort of evidence. But the only thing I've been able to find is this dubious blog post: https://lonesysadmin.net/2012/03/23/why-is-it-called-resilvering/

Q: Why do some people refer to the process of remirroring or rebuilding a RAID 1 drive set as “resilvering?”

A: Antique mirrors (the reflective kind you hang on a wall, or are in your bathroom) used silver (Ag) for the reflective coating, below the glass. Over time that silver would get tarnished and/or damaged, so you’d restore them by re-silvering them. I’m sure you’ve all seen this, where an old mirror has streaks in it but they’re below the glass. When your RAID 1 mirror set gets “tarnished” you resilver it and it’s shiny & new again. You can rebuild a RAID 5 array but you resilver a mirror. :)

With no real evidence. It might be correct. But I'd love to see some evidence or even confirmation/a different explanation from a more authoritative source.

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    The physical platters of a hard drive are usually very shiny so the mirror analogy isn't so far fetched.
    – KillingTime
    Aug 12, 2022 at 12:19
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    In my 45 years in computer engineering/programming I have never heard the term.
    – Hot Licks
    Aug 12, 2022 at 12:30
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    @HotLicks where do you work? Because this term is just incredibly standard when it comes to drive redundancy systems? It's used absolutely everywhere, and with ZFS at least it's the direct terminology used, but so is it in many hardware RAID systems, and it's insanely common on forums like reddit, SpiceWorks, etc. If you deal with any of these systems I don't know how you could miss it, but if you're a software developer (like you mentioned), then yeah of course this is pretty out of your domain.
    – Levi H
    Aug 12, 2022 at 13:14
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    @djs it's not remotely obscure at all? It's used extensively on topics like this, and is the officially adopted word on many platforms like ZFS, certain RAID cards, etc. And it's used pretty much constantly all over popular forums. And while I don't have 43 years exp, in my experience it's just common jargon used in the industry. What do you specifically do? Because as someone who has done a lot of mixed roles and semi-career changes (software dev, DevOps, system architect) I never heard it when I was a dev, but of course hear it all the time in the other two.
    – Levi H
    Aug 12, 2022 at 13:25
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    The blog post you quote seems to explain it all. It's a very obvious (once you know) connection of silvering with mirrors. If the first person to use the term thought it too obvious to need explaining, then there will be no evidence of its origin. Although I agree it's possible that the first person to use it might have felt the need to explain, they may well not have.
    – Stuart F
    Aug 12, 2022 at 14:48

1 Answer 1

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The mirror-related meaning is well-attested; Cambridge defines re-silver as:

to repair a mirror by covering the back of the glass with a new layer of silver-colored material

Since resilvering in computing refers to repairing mirrors of data, this is almost certainly the correct etymology.

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  • What's the earliest attestation? When did the term start to be used in this manner for drive arrays? Steve Gibson never used it, TTBOMK.
    – TimR on a different device
    Aug 22 at 21:55

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