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From "Hiller, Dean" <>
Subject Re: cassandra vs. mongodb quick question(good additional info)
Date Wed, 20 Feb 2013 20:20:08 GMT
Heh, we just discovered that mistake a few minutes ago….thanks though.  I am now wondering
and may run a test cluster with a separate 6 nodes and test how compaction is on very large
data sets and such.  We have tons of research data that sits there so I am wondering if 20T
/ node is now feasible with cassandra(I mean if mongodb has a 42T which 10gen was telling
my colleague, I would think we can with cassandra).

Is there any reasons I should know up front that 20T per node won't work.  We have 20 disks
per node and this definitely has a different profile than previous cassandra systems I have
setup.  We don't need really any caching as disk access is typically fine on reads.


From: Bryan Talbot <<>>
Reply-To: "<>" <<>>
Date: Wednesday, February 20, 2013 1:04 PM
To: "<>" <<>>
Subject: Re: cassandra vs. mongodb quick question(good additional info)

This calculation is incorrect btw.  10,000 GB transferred at 1.25 GB / sec would complete
in about 8,000 seconds which is just 2.2 hours and not 5.5 days.  The error is in the conversion
(1hr/60secs) which is off by 2 orders of magnitude since (1hr/3600secs) is the correct conversion.


On Mon, Feb 18, 2013 at 5:00 PM, Hiller, Dean <<>>
Google "10 gigabit in gigabytes" gives me 1.25 gigabytes/second  (yes I could have divided
by 8 in my head but eh…course when I saw the number, I went duh)

So trying to transfer 10 Terabytes  or 10,000 Gigabytes to a node that we are bringing online
to replace a dead node would take approximately 5 days???

This means no one else is using the bandwidth too ;).  10,000Gigabytes * 1 second/1.25 * 1hr/60secs
* 1 day / 24 hrs = 5.555555 days.  This is more likely 11 days if we only use 50% of the network.

So bringing a new node up to speed is more like 11 days once it is crashed.  I think this
is the main reason the 1Terabyte exists to begin with, right?

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