This is incorrect, as discussed a few weeks ago.  I have a setup with multiple
disks, and as soon as compaction occurs all the data ends up on one disk.  If
you need the additional io, you will want raid0.  But simply listing multiple
DataFileDirectories will not work.


On Wed, Mar 10, 2010 at 02:08:13AM -0600, Stu Hood wrote:
> 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
> Thanks,
> Stu
> -----Original Message-----
> From: "Eric Rosenberry" <>
> Sent: Wednesday, March 10, 2010 2:00am
> To:
> 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

Anthony Molinaro                           <>

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