Re: RAID controllers for Postgresql on large setups

On Tue, May 13, 2008 at 8:00 AM, Francisco Reyes <lists(at)stringsutils(dot)com> wrote:
> PFC writes:
>
>
> > You say that like you don't mind having PCI in a server whose job
> is to perform massive query over large data sets.
> >
>
> I am in my 4th week at a new job. Trying to figure what I am working with.
> From what I see I will likely get as much improvement from new hardware as
> from re-doing some of the database design. Can't get everything done at
> once, not to mention I have to redo one machine sooner rather than later so
> I need to prioritize.
>
>
>
> > In fact for bulk IO a box with 2 SATA drives would be just as fast as
> your monster RAID, lol.
> >
>
> I am working on setting up a standard test based on the type of operations
> that the company does. This will give me a beter idea. Specially I will work
> with the developers to make sure the queries I create for the benchmark are
> representative of the workload.
>
>
>
> > Adding more drives will help random reads/writes but do nothing for
> throughput since the tiny PCI pipe is choking.
> >
>
> Understood, but right now I have to use the hardware they already have.
> Just trying to make the most of it. I believe another server is due in some
> months so then I can better plan.
>
> In your opinion if we get a new machine with PCI-e, at how many spindles
> will the SCSI random access superiority start to be less notable? Specially
> given the low number of connections we usually have running against these
> machines.
>
>
>
> > However RAID5 will choke and burn on small random writes, which
> will come from UPDATing random rows in a large table, updating indexes,
> etc. Since you are doing this apparently, RAID5 is therefore NOT advised !
> >
>
> I thought I read a while back in this list that as the number of drives
> increased that RAID 5 was less bad. Say an external enclosure with 20+
> drives.

maybe, but I don't think very many people run that many drives in a
raid 5 configuration...too dangerous. with 20 drives in a single
volume, you need to be running raid 10 or raid 6. 20 drive raid 50 is
pushing it as well..I'd at least want a hot spare.

merlin