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From aaron morton <aa...@thelastpickle.com>
Subject Re: Disk configuration in new cluster node
Date Tue, 18 Sep 2012 08:54:31 GMT
> Given the advice to use a single RAID 0 volume, I think that's what I'll do.  By system
mirror, you are referring to the volume on which the OS is installed? 
Yes. 
I was thinking about a simple RAID 1 OS volume and RAID 0 data volume setup. With the Commit
Log on the OS volume so it does not compete with cassandra for iops.  
 
> sense in my case to build or maintain a large cluster.  I wanted to run a two-node setup
(RF=1, RCL=ONE, WCL=ALL),
You would be taking on the operational concerns of running cassandra without any of the payoff
for having a cluster. 

> each with several disks having large capacity, totaling 10 - 12 TB.  Is this (another)
bad idea?
Yes. Very bad. 
If you had 6TB on average system with spinning disks you would measure duration of repairs
and compactions in days. 

If you want to store 12 TB of data you will need more machines. 
 
Hope that helps. 

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

On 18/09/2012, at 3:53 AM, Casey Deccio <casey@deccio.net> wrote:

> On Mon, Sep 17, 2012 at 1:19 AM, aaron morton <aaron@thelastpickle.com> wrote:
>>  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.
> 
> 
> Given the advice to use a single RAID 0 volume, I think that's what I'll do.  By system
mirror, you are referring to the volume on which the OS is installed?  Should the volume with
the commit log also have multiple disks in a RAID 0 volume?  Alternatively, would a RAID 1
setup be reasonable for the system volume/OS, so the system itself can be resilient to disk
failure, or would that kill commit performance?
> 
> Any preference to hardware RAID 0 vs. using something like mdadm?
> 
> 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.
> 
> Hmm.  My hope was to be able to run a minimal number of nodes and maximize their capacity
because it doesn't make sense in my case to build or maintain a large cluster.  I wanted to
run a two-node setup (RF=1, RCL=ONE, WCL=ALL), each with several disks having large capacity,
totaling 10 - 12 TB.  Is this (another) bad idea?
> 
> Casey


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