Date: Sat, 03 Jun 2006 12:13:27 +1200
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: RES: Initial database loading and IDE x SCSI
In-reply-to: <1149279209.20798.108.camel@archimedes>
To: carlosreimer@terra.com.br
Cc: Mark Lewis <mark.lewis@mir3.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	pgsql-performance@postgresql.org
Message-id: <4480D427.50207@paradise.net.nz>
MIME-version: 1.0
Content-type: text/plain; format=flowed; charset=UTF-8
Content-transfer-encoding: 7bit
User-Agent: Thunderbird 1.5 (X11/20060417)
References: <PEEPKDFEHHEMKBBFPOOKCEHFCPAA.carlosreimer@terra.com.br>
	<1149279209.20798.108.camel@archimedes>

Mark Lewis wrote:

> 
> The naive approach works on IDE drives because they don't (usually)
> honor the request to write the data immediately, so it can fill its
> write cache up with several megabytes of data and write it out to the
> disk at its leisure.
> 

FWIW - If you are using MacOS X or Windows, then later SATA (in 
particular, not sure about older IDE) will honor the request to write 
immediately, even if the disk write cache is enabled.

I believe that Linux 2.6+ and SATA II will also behave this way (I'm 
thinking that write barrier support *is* in 2.6 now - however you would 
be wise to follow up on the Linux kernel list if you want to be sure!)

In these cases data integrity becomes similar to SCSI - however, unless 
you buy SATA specifically designed for a server type workload (e.g WD 
Raptor), then ATA/SATA tend to fail more quickly if used in this way 
(e.g. 24/7, hot/dusty environment etc).

Cheers

Mark