Re: Poor performance on SCSI machines, good on IDE?

On Fri, 16 Nov 2001, Eric Crampton wrote:

> I'm seeing some strange performance behavior with PostgreSQL. In the
> following four examples, I'm using the PGDG RPMs on Redhat Linux
> 7.2. On the machines with IDE disks, I'm seeing *MUCH* faster INSERTs
> than the machines with SCSI. I'm trying to figure out why. Disk
> benchmarking programs show the SCSI machines should have much faster
> seek and transfer times.

I guess your IDE disks are set to write caching enabled. You can turn
this off (in theory) with

    hdparm -W 0 /dev/hd?

(cf. man-page to hdparm)

Note that not all IDE drives support turning off write caching, most will
do write-caching irregardless of the setting of this flag (with obvious
consequences with respect to data integrity on the one hand and performance
on the other hand).

Regards
--
Helge Bahmann <bahmann@math.tu-freiberg.de>             /| \__
Network admin, systems programmer                      /_|____\
                                                     _/\ |   __)
$ ./configure                                        \\ \|__/__|
checking whether build environment is sane... yes     \\/___/ |
checking for AIX... no (we already did this)            |