Then what will be the sweetspot for Cassandra? I am more interested in Cassandra because my application is write heavy.

Till now what I have understood is that Cassandra will not work best for SANs too?

Mongodb is also a nosql database and designed for horizontal scaling then how its good for the same hardware for which Cassandra is not a good candidate?

----- Original Message -----
From: Bill <>
Sent: Sunday, September 4, 2011 4:34 AM
Subject: Re: commodity server spec

[100% agree with Chris]

China, the machines you're describing sound nice for mongodb/postgres/mysql, but probably not the sweetspot for Cassandra.

Obviously (well depending on near term load) you don't want to get burned on excess footprint. But a realistic, don't lose data, be fairly available deployment is going to span at least 2 racks/power supplies and have data replicated offsite (at least as passive for DR). So I would consider 6-9 relatively weaker servers rather than 3 scale up joints. You'll save some capex, and the amount of opex overhead is probably worth it traded off against the operational risk. 3 is an awkward number to operate for anything that needs to be available (although many people seem to start with that, I am guessing because triplication is traditionally understood under failure) as it immediately puts 50% extra load on the remaining 2 when one node goes away. One will go away, even transiently, when it is upgraded, crashes, gets into a funk due to compaction or garbage collection, and load will then be shunted onto the other 2 - remember Cassandra has no backoff/throttling in place. I'd allow for something breaking at some point (dbs even the mature ones, fail from time to time) and 2 doesn't give you much room to maneuver in production.


On 03/09/11 23:05, Chris Goffinet wrote:
> It will also depend on how long you can handle recovery time. So imagine
> this case:
> 3 nodes w/ RF of 3
> Each node has 30TB of space used (you never want to fill up entire node).
> If one node fails and you must recover, that will take over 3.6 days in
> just transferring data alone. That's with a sustained 800megabit/s
> (100MB/s). In the real world it's going to fluctuate so add some
> padding. Also, since you will be saturating one of the other nodes, now
> you're network latency performance is suffering and you only have 1
> machine to handle the remaining traffic while you're recovering. And if
> you want to expand the cluster in the future (more nodes), the amount of
> data to transfer is going to be very large and most likely days to add
> machines. From my experience it's must better to have a larger cluster
> setup upfront for future growth than getting by with 6-12 nodes at the
> start. You will feel less pain, easier to manage node failures (bad
> disks, mem, etc).
> 3 nodes with RF of 1 wouldn't make sense.
> On Sat, Sep 3, 2011 at 4:05 AM, China Stoffen <
> <>> wrote:
>    Many small servers would drive up the hosting cost way too high so
>    want to avoid this solution if we can.
>    ----- Original Message -----
>    From: Radim Kolar < <>>
>    To: <>
>    Cc:
>    Sent: Saturday, September 3, 2011 9:37 AM
>    Subject: Re: commodity server spec
>    many smaller servers way better