On Mon, Mar 3, 2008 at 8:48 AM, Mark Mielke <mark@xxxxxxxxxxxxxx> wrote: > Matthew wrote: > > On Sat, 1 Mar 2008, Craig James wrote: > >> Right, I do understand that, but reliability is not a top priority in > >> this system. The database will be replicated, and can be reproduced > >> from the raw data. > > > > So what you're saying is: > > > > 1. Reliability is not important. > > 2. There's zero write traffic once the database is set up. > > > > If this is true, then RAID-0 is the way to go. I think Greg's options > > are good. Either: > > > > 2 discs RAID 1: OS > > 6 discs RAID 0: database + WAL > > > > which is what we're using here (except with more discs), or: > > > > 8 discs RAID 10: everything > > Has anybody been able to prove to themselves that RAID 0 vs RAID 1+0 is > faster for these sorts of loads? My understanding is that RAID 1+0 *can* > reduce latency for reads, but that it relies on random access, whereas > RAID 0 performs best for sequential scans? Does PostgreSQL ever do > enough random access to make RAID 1+0 shine? RAID 1+0 has certain theoretical advantages in parallel access scenarios that straight RAID-0 wouldn't have. I.e. if you used n>2 disks in a mirror and built a RAID-0 out of those types of mirrors, then you could theoretically have n users reading data on the same "drive" (the raid-1 underneath the raid-0) at the same time where RAID-0 would only have the one disk to read from. The effects of this advantage are dulled by caching, depending on how much of the data set you can cache. With a system that can cache it's whole data set in memory (not uncommon for transactional systems) or at least a large percentage, the n>2 RAID-1 sets aren't that big of an advantage. RAID-0 of n drives should behave pretty similarly to RAID-10 with 2n drives for most types of access. I.e. no better or worse for sequential or random access, if the number of drives is equivalent. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.org&extra=pgsql-performance
