[erlang-questions] erlang-questions Digest, Vol 249, Issue 1

Mark Steele mark@REDACTED
Mon Dec 21 17:37:04 CET 2015

> ------------------------------
> Message: 4
> Date: Mon, 21 Dec 2015 15:12:04 +1300
> From: <ok@REDACTED>
> To: zxq9 <zxq9@REDACTED>
> Cc: erlang-questions@REDACTED
> Subject: Re: [erlang-questions] Streaming a folder from one node to
>         another
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>         <d2b337fe0720dc9ecefbcbb469661933.squirrel@REDACTED>
> Content-Type: text/plain; charset="iso-8859-1"
> Re streaming an arbitrarily large folder from one node to another
> in a cluster:
> 1. Why is it necessary to do this?
>    Why is it impossible or undesirable to just serve blocks from
>    the files to the other node on demand?
To backup data in a sharded distributed system from a central point.

> 2. You seem to be suggesting that it is necessary to communicate
>    the whole thing in one go.  Why is it not possible to set up
>    a common initial state and stream changes?
Yes I am. There is no shared initial state.

> 3. What are you going to do if the contents of the folder change
>    faster than you can stream them?
Data files are immutable once written, with a bit of coordination it's
possible to get a point in time snapshot.

> 4. I'm wondering about the cost of streaming vs the cost of simply
>    switching the storage device from one node's control to
>    another's.  (In the extreme, getting a human to swap cables.
>    I mean, that could take just seconds.  Electronic switching would
>    likely be better.  And yes, I'm thinking of old "truck of tapes"
>    ideas.)  Surely the cluster is equipped to switch devices from
>    one CPU board to another in order to handle CPU board failure...
This speculation is not relevant..
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