On 3/2/07, Ron <rjpeace@xxxxxxxxxxxxx> wrote:
At 02:43 PM 3/2/2007, Alex Deucher wrote: >On 3/2/07, Ron <rjpeace@xxxxxxxxxxxxx> wrote: >> >>...and I still think looking closely at the actual physical layout of >>the tables in the SAN is likely to be worth it. > >How would I go about doing that? > >Alex Hard for me to give specific advice when I don't know what SAN product we are talking about nor what kind of HDs are in it nor how those HDs are presently configured... I quote you in an earlier post: "The RAID groups on the SAN were set up for maximum capacity rather than for performance. Using it for the databases just came up recently." That implies to me that the SAN is more or less set up as a huge 105 HD (assuming this number is correct? We all know how "assume" is spelled...) JBOD or RAID 5 (or 6, or 5*, or 6*) set. =IF= that is true, tables are not being given dedicated RAID groups. That implies that traditional lore like having pg_xlog on dedicated spindles is being ignored. Nor is the more general Best Practice of putting the most heavily used tables onto dedicated spindles being followed. In addition, the most space efficient RAID levels: 5* or 6*, are not the best performing one (RAID 10 striping your mirrors) In short, configuring a SAN for maximum capacity is exactly the wrong thing to do if one is planning to use it in the best way to support DB performance. I assume (there's that word again...) that there is someone in your organization who understands how the SAN is configured and administered. You need to talk to them about these issues.
Ah OK. I see what you are saying; thank you for clarifying. Yes, the SAN is configured for maximum capacity; it has large RAID 5 groups. As I said earlier, we never intended to run a DB on the SAN, it just happened to come up, hence the configuration. Alex
