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From "Stu Hood" <stu.h...@rackspace.com>
Subject RE: Effective allocation of multiple disks
Date Wed, 10 Mar 2010 08:08:13 GMT
You can list multiple DataFileDirectories, and Cassandra will scatter files across all of them.
Use 1 disk for the commitlog, and 3 disks for data directories.

See http://wiki.apache.org/cassandra/CassandraHardware#Disk

Thanks,
Stu

-----Original Message-----
From: "Eric Rosenberry" <eprosenx@gmail.com>
Sent: Wednesday, March 10, 2010 2:00am
To: cassandra-user@incubator.apache.org
Subject: Effective allocation of multiple disks

Based on the documentation, it is clear that with Cassandra you want to have
one disk for commitlog, and one disk for data.

My question is: If you think your workload is going to require more io
performance to the data disks than a single disk can handle, how would you
recommend effectively utilizing additional disks?

It would seem a number of vendors sell 1U boxes with four 3.5 inch disks.
 If we use one for commitlog, is there a way to have Cassandra itself
equally split data across the three remaining disks?  Or is this something
that needs to be handled by the hardware level, or operating system/file
system level?

Options include a hardware RAID controller in a RAID 0 stripe (this is more
$$$ and for what gain?), or utilizing a volume manager like LVM.

Along those same lines, if you do implement some type of striping, what RAID
stripe size is recommended?  (I think Todd Burruss asked this earlier but I
did not see a response)

Thanks for any input!

-Eric



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