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