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From Ran User <ranuse...@gmail.com>
Subject Re: idea drive layout - 4 drives + RAID question
Date Wed, 31 Oct 2012 00:11:37 GMT
Is there a concern of a large falloff in commit log write performance
(sequential) when sharing 2 drives (RAID 1) with the OS (os and services
writing their own logs, etc)?  Do you expect the hit to be marginal?


On Tue, Oct 30, 2012 at 7:58 PM, aaron morton <aaron@thelastpickle.com>wrote:

> We also have 4-disk nodes, and we use the following layout:****
> 2 x OS + Commit in RAID 1****
> 2 x Data disk in RAID 0
>
> +1
>
> You are replicating data at the application level and want the fastest
> possible IO performance per node.
>
>  You can already distribute the
> individual Cassandra column families on different drives by just
> setting up symlinks to the individual folders.
>
> There are some features coming in 1.2 that make using a JBOD setup easier.
>
> Cheers
>
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 30/10/2012, at 9:23 PM, Pieter Callewaert <
> pieter.callewaert@be-mobile.be> wrote:
>
> We also have 4-disk nodes, and we use the following layout:****
> 2 x OS + Commit in RAID 1****
> 2 x Data disk in RAID 0****
>
> This gives us the advantage we never have to reinstall the node when a
> drive crashes.****
>
> Kind regards,****
> Pieter****
>
>
> *From:* Ran User [mailto:ranuser99@gmail.com]
> *Sent:* dinsdag 30 oktober 2012 4:33
> *To:* user@cassandra.apache.org
> *Subject:* Re: idea drive layout - 4 drives + RAID question****
>
> Have you considered running RAID 10 for the data drives to improve MTBF?
> ****
>  ****
> On one hand Cassandra is handling redundancy issues, on the other
> hand, reducing the frequency of dealing with failed nodes
> is attractive if cheap (switching RAID levels to 10). ****
>  ****
>
> We have no experience with software RAID (have always used hardware raid
> with BBU).  I'm assuming software RAID 1 or 10 (the mirroring part) is
> inherently reliable (perhaps minus some edge case).****
> On Tue, Oct 30, 2012 at 1:07 AM, Tupshin Harper <tupshin@tupshin.com>
> wrote:****
>
> I would generally recommend 1 drive for OS and commit log and 3 drive raid
> 0 for data. The raid does give you good performance benefit, and it can be
> convenient to have the OS on a side drive for configuration ease and better
> MTBF.****
>
> -Tupshin****
> On Oct 29, 2012 8:56 PM, "Ran User" <ranuser99@gmail.com> wrote:****
> I was hoping to achieve approx. 2x IO (write and read) performance via
> RAID 0 (by accepting a higher MTBF).****
>  ****
> Do believe the performance gains of RAID0 are much lower and/or are not
> worth it vs the increased server failure rate?****
>  ****
> From my understanding, RAID 10 would achieve the read performance benefits
> of RAID 0, but not the write benefits.  I'm also considering RAID 10 to
> maximize server IO performance. ****
>  ****
> Currently, we're working with 1 CF.****
>  ****
>  ****
>
> Thank you****
> On Mon, Oct 29, 2012 at 11:51 PM, Timmy Turner <timm.turn@gmail.com>
> wrote:****
> I'm not sure whether the raid 0 gets you anything other than headaches
> should one of the drives fail. You can already distribute the
> individual Cassandra column families on different drives by just
> setting up symlinks to the individual folders.
>
> 2012/10/30 Ran User <ranuser99@gmail.com>:****
> > For a server with 4 drive slots only, I'm thinking:
> >
> > either:
> >
> > - OS (1 drive)
> > - Commit Log (1 drive)
> > - Data (2 drives, software raid 0)
> >
> > vs
> >
> > - OS  + Data (3 drives, software raid 0)
> > - Commit Log (1 drive)
> >
> > or something else?
> >
> > also, if I can spare the wasted storage, would RAID 10 for cassandra data
> > improve read performance and have no effect on write performance?
> >
> > Thank you!****
> ** **
>
>
>

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