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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Multiple large disks in server - setup considerations
Date Tue, 31 May 2011 18:23:36 GMT
Have you read http://wiki.apache.org/cassandra/CassandraHardware ?

On Tue, May 31, 2011 at 7:47 AM, Erik Forsberg <forsberg@opera.com> wrote:
> Hi!
>
> I'm considering setting up a small (4-6 nodes) Cassandra cluster on
> machines that each have 3x2TB disks. There's no hardware RAID in the
> machine, and if there were, it could only stripe single disks
> together, not parts of disks.
>
> I'm planning RF=2 (or higher).
>
> I'm pondering what the best disk configuration is. Two alternatives:
>
> 1) Make small partition on first disk for Linux installation and commit
>   log. Use Linux' software RAID0 to stripe the remaining space on disk1
>   + the two remaining disks into one large XFS partition.
>
> 2) Make small partition on first disk for Linux installation and commit
>   log. Mount rest of disk 1 as /var/cassandra1, then disk2
>   as /var/cassandra2 and disk3 as /var/cassandra3.
>
> Is it unwise to put the commit log on the same physical disk as some of
> the data? I guess it could impact write performance, but maybe it's bad
> from a data consistency point of view?
>
> How does Cassandra handle replacement of a bad disk in the two
> alternatives? With option 1) I guess there's risk of files being
> corrupt. With option 2) they will simply be missing after replacing the
> disk with a new one.
>
> With option 2) I guess I'm limiting the size of the total amount of
> data in the largest CF at compaction to, hmm.. the free space on the
> disk with most free space, correct?
>
> Comments welcome!
>
> Thanks,
> \EF
> --
> Erik Forsberg <forsberg@opera.com>
> Developer, Opera Software - http://www.opera.com/
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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