Thanks. Yep, I think OS + CL (2 drive RAID1) will provide the best balance of reduced headaches / performance. I'll also be pondering 1 drive OS, 1 drive CL as well. On Wed, Oct 31, 2012 at 9:27 PM, aaron morton <aa...@thelastpickle.com>wrote:
> Good question. > > The is a comment on the DS blog or docs somewhere that says on EC2 running > the commit log on the raid-0 ephemeral is preferred. I think the > recommendation was specifically about how the disks are setup on EC2. > > While the commit log will be competing with logs and everything else on > the OS volume, it would be competing with C* reads, Memtable flushing, > compacting and repairing on the data volume. > > The only way to be sure is to test both setups. > > Cheers > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 31/10/2012, at 1:11 PM, Ran User <ranuse...@gmail.com> wrote: > > 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!**** >> ** ** >> >> >> > >
