Commit log + Data directory on same partition (software raid)

[Thibaut Britz <th...@trendiction.com>]

Hi,

Has anyone of you made some experience with software raid (raid 1,
mirroring 2 disks)?

Our workload is rather read based at the moment (Commit Log directory only
grows by 128MB every 2-3 minutes), while the second hd is under high load
due to the read requests to our cassandra cluster.

I was thinking about putting both the commit log and the data directory on
a software raid partition spanning over the two disks. Would this increase
the general read performance? In theory I could get twice the read
performance, but I don't know how the commit log will influence the read
performance on both disks?

Thanks,
Thibaut

Re: Commit log + Data directory on same partition (software raid)

[Tom Duffield <to...@gmail.com>]

Having the both the commit log and data directory on the same volume is
generally not recommended. You would actually see a performance decrease
unless you can have most your reads be cache hits.

On Friday, August 10, 2012, Thibaut Britz wrote:

> Hi,
>
> Has anyone of you made some experience with software raid (raid 1,
> mirroring 2 disks)?
>
> Our workload is rather read based at the moment (Commit Log directory only
> grows by 128MB every 2-3 minutes), while the second hd is under high load
> due to the read requests to our cassandra cluster.
>
> I was thinking about putting both the commit log and the data directory on
> a software raid partition spanning over the two disks. Would this increase
> the general read performance? In theory I could get twice the read
> performance, but I don't know how the commit log will influence the read
> performance on both disks?
>
> Thanks,
> Thibaut
>
>

Re: Commit log + Data directory on same partition (software raid)

[Thibaut Britz <th...@trendiction.com>]

Unfortunately ssd drives are no option at the moment. I have to use 2
regular hds. Has anyone tried above scenario?

THanks,
Thibaut


On Fri, Aug 10, 2012 at 3:30 PM, Radim Kolar <hs...@filez.com> wrote:

>
>  I was thinking about putting both the commit log and the data directory
>> on a software raid partition spanning over the two disks. Would this
>> increase the general read performance? In theory I could get twice the read
>> performance, but I don't know how the commit log will influence the read
>> performance on both disks?
>>
> zfs + ssd cache is best. get freebsd 8.3 and install cassandra from ports.
>
>

Re: Commit log + Data directory on same partition (software raid)

[Radim Kolar <hs...@filez.com>]

> I was thinking about putting both the commit log and the data 
> directory on a software raid partition spanning over the two disks. 
> Would this increase the general read performance? In theory I could 
> get twice the read performance, but I don't know how the commit log 
> will influence the read performance on both disks?
zfs + ssd cache is best. get freebsd 8.3 and install cassandra from ports.