From: William Yu <wyu@talisys.com>
Subject: Re: Help specifying new web server/database machine
Date: Wed, 08 Jun 2005 16:33:21 -0700
Organization: Hub.Org Networking Services
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Message-ID: <d87v84$2ihi$1@news.hub.org>
References: <20050608163418.GA3327@campbell-lange.net>
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In-Reply-To: <20050608163418.GA3327@campbell-lange.net>
To: pgsql-performance@postgresql.org

> We are considering two RAID1 system disks, and two RAID1 data disks.
> We've avoided buying Xeons. The machine we are looking at looks like
> this:
> 
>     Rackmount Chassis - 500W PSU / 4 x SATA Disk Drive Bays
>     S2882-D - Dual Opteron / AMD 8111 Chipset / 5 x PCI Slots
>     2x - (Dual) AMD Opteron 246 Processors (2.0GHz) - 1MB L2 Cache/core (single core)

For about $1500 more, you could go 2x270 (dual core 2ghz) and get a 4X 
SMP system. (My DC 2x265 system just arrived -- can't wait to start 
testing it!!!)

>     2GB (2x 1024MB) DDR-400 (PC3200) ECC Registered SDRAM (single rank)

This is a wierd configuration. For a 2x Opteron server to operate at max 
performance, it needs 4 DIMMs minimum. Opterons use a 128-bit memory 
interface and hence requires 2 DIMMs per CPU to run at full speed. With 
only 2 DIMMS, you either have both CPUs run @ 64-bit (this may not even 
be possible) or populate only 1 CPU bank -- the other CPU must then 
request all memory access through the other CPU which is a significant 
penalty. If you went 4x512MB, you'd limit your future update options by 
having less slots available to add more memory. I'd definitely out of 
the chute get 4x1GB,

>     4 Port AMCC/3Ware 9500-4LP PCI SATA RAID Controller
>     80GB SATA-150 7200RPM Hard Disk / 8MB Cache
>     80GB SATA-150 7200RPM Hard Disk / 8MB Cache
>     250GB SATA-150 7200RPM Hard Disk / 8MB Cache
>     250GB SATA-150 7200RPM Hard Disk / 8MB Cache

Now this is comes to the interesting part. We've had huge, gigantic 
threads (check archives for the $7K server threads) about SCSI versus 
SATA in the past. 7200 SATAs just aren't fast/smart enough to cut it for 
most production uses in regular configs. If you are set on SATA, you 
will have to consider the following options: (1) use 10K Raptors for TCQ 
goodness, (2) put a huge amount of memory onto the SATA RAID card -- 1GB 
minimum, (3) use a ton of SATA drives to make a RAID10 array -- 8 drives 
minimum.

Or you could go SCSI. SCSI is cost prohibitive though at the larger disk 
sizes -- this is why I'm considering option #3 for my data processing 
server.