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From aaron morton <aa...@thelastpickle.com>
Subject Re: Disk configuration in new cluster node
Date Mon, 17 Sep 2012 08:19:26 GMT
>  4 drives for data and 1 drive for commitlog, 
How are you configuring the drives ? It's normally best to present one big data volume, e.g.
using raid 0, and put the commit log on say the system mirror.

> will the node balance out the load on the drives, or is it agnostic to usage of drives
underlying data directories?
It will not. 
There is a feature coming in v1.2 to add better support for JBOD configurations. 

A word of warning. If you put more than 300GB to 400GB per node you may end experience some
issues such as repair, compaction or disaster recovery taking a long time. These are simply
soft limits that provide a good rule of thumb for HDD based systems with 1 GigE networking.
  

Hope that helps. 
-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 15/09/2012, at 7:39 AM, Casey Deccio <casey@deccio.net> wrote:

> I'm building a new "cluster" (to replace the broken setup I've written about in previous
posts) that will consist of only two nodes.  I understand that I'll be sacrificing high availability
of writes if one of the nodes goes down, and I'm okay with that.  I'm more interested in maintaining
high consistency and high read availability.  So I've decided to use a write-level consistency
of ALL and read-level consistency of ONE.
> 
> My first question is about the drives in this setup.  If I initially set up the system
with, say, 4 drives for data and 1 drive for commitlog, and later I decide to add more capacity
to the node by adding more drives for data (adding the new data directory entries in cassandra.yaml),
will the node balance out the load on the drives, or is it agnostic to usage of drives underlying
data directories?
> 
> My second question has to do with RAID striping.  Would it be more useful to stripe the
disk with the commitlog or the disks with the data?  Of course, with a single striped volume
for data directories, it would be more difficult to add capacity to the node later, as I've
suggested above.
> 
> Casey


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