On Tue, 21 Oct 2003, Josh Berkus wrote:

> Anjan,
> > Pretty soon, a PowerEdge 6650 with 4 x 2Ghz XEONs, and 8GB Memory, with
> > internal drives on RAID5 will be delivered. Postgres will be from RH8.0.
> How many drives?   RAID5 sucks for heavy read-write databases, unless you have 
> 5+ drives.  Or a large battery-backed cache.

You don't need a large cache, so much as a cache.  The size isn't usually 
an issue now that 64 to 256 megs caches are the nominal cache sizes.  Back 
when it was a choice of 4 or 8 megs it made a much bigger difference than 
64 versus 256 meg make today.

Also, if it's a read only environment, RAID5 with n drives equals the 
performance of RAID0 with n-1 drives.

> Also, last I checked, you can't address 8GB of RAM without a 64-bit processor.  
> Since when are the Xeons 64-bit?

Josh, you gotta get out more.  IA32 has supported >4 gig ram for a long 
time now, and so has the linux kernel.  It uses a paging method to do it.  
Individual processes are still limited to ~3 gig on Linux on 32 bit 
hardware though, so the extra mem will almost certainly spend it's time as 
kernel cache.

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