On Tue, 2006-08-08 at 17:53, Thomas F. O'Connell wrote: > On Aug 8, 2006, at 5:28 PM, Joshua D. Drake wrote: > > > Thomas F. O'Connell wrote: > >> On Aug 8, 2006, at 4:49 PM, Joshua D. Drake wrote: > >>>> I am considering a setup such as this: > >>>> - At least dual cpu (possibly with 2 cores each) > >>>> - 4GB of RAM > >>>> - 2 disk RAID 1 array for root disk > >>>> - 4 disk RAID 1+0 array for PGDATA > >>>> - 2 disk RAID 1 array for pg_xlog > >>>> Does anyone know a vendor that might be able provide such setup? > >> Wouldn't it be preferable to put WAL on a multi-disk RAID 10 if > >> you had the opportunity? This gives you the redundancy of RAID 1 > >> but approaches the performance of RAID 0, especially as you add > >> disks to the array. In benchmarking, I've seen consistent success > >> with this approach. > > > > WALL is written in order so RAID 1 is usually fine. We also don't > > need journaling for WAL so the speed is even faster. > > In which case, which is theoretically better (since I don't have a > convenient test bed at the moment) for WAL in a write-heavy > environment? More disks in a RAID 10 (which should theoretically > improve write throughput in general, to a point) or a 2-disk RAID 1? > Does it become a price/performance question, or is there virtually no > benefit to throwing more disks at RAID 10 for WAL if you turn off > journaling on the filesystem? Actually, the BIGGEST win comes when you've got battery backed cache on your RAID controller. In fact, I'd spend money on a separate RAID controller for xlog with its own cache hitting a simple mirror set before I'd spring for more drives on pg_xlog. The battery backed cache on the pg_xlog likely wouldn't need to be big, just there and set to write-back. Then put all the rest of your cash into disks on a big RAID 10 config, and as big of a battery backed cache as you can afford for it and memory for the machine.
