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 <aa...@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.callewa...@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:ranuse...@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 <tups...@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" <ranuse...@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.t...@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 <ranuse...@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!**** > ** ** > > >
