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From aaron morton <>
Subject Re: Migration question
Date Thu, 16 Jun 2011 10:28:38 GMT
Lots of folk use a single disk or raid-1 for the system and commit log and raid-0 for the data

Your money is probably better spent on more nodes with more disks and more memory. More nodes
is always better.  

Happy to hear reasons otherwise. 


Aaron Morton
Freelance Cassandra Developer

On 15 Jun 2011, at 15:50, Marcos Ortiz wrote:

> El 6/14/2011 1:43 PM, Eric Czech escribió:
>> Thanks Aaron.  I'll make sure to copy the system tables.
>> Another thing -- do you have any suggestions on raid configurations for main data
drives?  We're looking at RAID5 and 10 and I can't seem to find a convincing argument one
way or the other.
> Well, I learned from administrating other databases (like PostgreSQL and Oracle) that
RAID 10 is the best solution for data. With RAID 5, the discs suffer a lot for the excesive
I/O and It can arrive to 
> data lost. You can search about the "RAID 5 Write Hole" to view this.
>> Thanks again for your help.
>> On Mon, Jun 6, 2011 at 5:45 AM, aaron morton <> wrote:
>> Sounds like you are OK to turn off the existing cluster first.
>> Assuming so, deliver any hints using JMX then do a nodetool flush to write out all
the memtables and checkpoint the commit logs. You can then copy the data directories.
>> The System data directory contains the nodes token and the schema, you will want
to copy this directory. You may also want to copy the cassandra.yaml or create new ones with
the correct initial tokens.
>> The nodes will sort themselves out when they start up and get new IP's, the important
thing to them is the token.
>> Cheers
>> -----------------
>> Aaron Morton
>> Freelance Cassandra Developer
>> @aaronmorton
>> On 6 Jun 2011, at 23:25, Eric Czech wrote:
>> > Hi, I have a quick question about migrating a cluster.
>> >
>> > We have a cassandra cluster with 10 nodes that we'd like to move to a new DC
and what I was hoping to do is just copy the SSTables for each node to a corresponding node
in the new DC (the new cluster will also have 10 nodes).  Is there any reason that a straight
file copy like this wouldn't work?  Do any system tables need to be moved as well or is there
anything else that needs to be done?
>> >
>> > Thanks!
> -- 
> Marcos Luís Ortíz Valmaseda
>  Software Engineer (UCI)

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