For Cassandra testing I am using a very old server with a one core Celeron processor and 1GiB RAM, and another one with 4GiB and 4 cores, both with two consumer SATA hard disks. Both works, i.e. there is no out of memory error etc. There are about 10 writes and reads per second, maybe more, but not more than 40. The "database" size was extremely small even after a few days, about 50 megabytes. The configuration is absolute stock configuration, I have not changed anything, except separating the LOG and DATA disk. 

This was a noticable node on the small server, I do not remember, somewhere between 0.1-0.5. On the other hand it was not noticable on the larger server.

It was interesting that the disk IO is higher on the LOG hard disk,  which also contained the system, than on the DATA disk.

Take these with a grain of salt, my intention was to test setting up a cluster in two distant datacenters, not to do some performance test.




On 2012.03.01. 11:26, Ertio Lew wrote:
expensive :-) I was expecting to start with 2GB nodes, if not 1GB for intial.

On Thu, Mar 1, 2012 at 3:43 PM, aaron morton <aaron@thelastpickle.com> wrote:
As others said, depends on load and traffic and all sorts of thins. 

if you want a number, 4Gb would me a reasonable minimum IMHO. (You may get by with less).  8Gb is about the tops. 
Any memory not allocated to Cassandra  will be used to map files into memory. 

If you can get machines with 8GB ram thats a reasonable start.

-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 1/03/2012, at 1:16 AM, Maki Watanabe wrote:

Depends on your traffic :-)

cassandra-env.sh will try to allocate heap with following formula if
you don't specify MAX_HEAP_SIZE.
1. calculate 1/2 of RAM on your system and cap to 1024MB
2. calculate 1/4 of RAM on your system and cap to 8192MB
3. pick the larger value

So how about to start with the default? You will need to monitor the
heap usage at first.

2012/2/29 Ertio Lew <ertiop93@gmail.com>:
Thanks, I think I don't need high consistency(as per my app requirements) so
I might be fine with CL.ONE instead of quorum, so I think  I'm probably
going to be ok with a 2 node cluster initially..

Could you guys also recommend some minimum memory to start with ? Of course
that would depend on my workload as well, but that's why I am asking for the
min


On Wed, Feb 29, 2012 at 7:40 AM, Maki Watanabe <watanabe.maki@gmail.com>
wrote:

If you run your service with 2 node and RF=2, your data will be
replicated but
your service will not be redundant. ( You can't stop both of nodes )

If your service doesn't need strong consistency ( allow cassandra returns
"old" data after write, and possible write lost ), you can use CL=ONE
for read and write
to keep availability.

maki





--
w3m