Re: Sobre performance

Excerpts from Horacio Miranda's message of jue oct 21 05:15:31 -0300 2010:

> Al comprar un nuevo disco duro para mi laptop, el performance decia
> que el WD era el doble que el seagate de 7200 que tengo, luego me puse
> a jugar con las particiones y a repetir las pruebas de iometer y Hp
> tune pro y me di cuenta que la diferencia entre IO de una particion
> que esta al comienzo del disco puede marcar 105 MB/s y una que esta al
> final 50 MB/s

Greg Smith está de acuerdo contigo. Dice en el capítulo 3 de
"PostgreSQL 9.0 High Performance"

Disk performance expectations

So what are the reasonable expectations for how your disks
should perform? The last example shown demonstrates how things
should work. Any good drive nowadays should have sequential
transfers of well over 50 MB/s on its fastest area, with 100
MB/s being easy to find. The slowest part of the drive will be
closer to half that speed.

> O hacerlo todo con LVM.

Poor or excessive mapping of your physical disk to how the
operating system sees them can also slow down results by more
than you might expect. For example, passing through Linux's LVM
layer can cause a 10-20% speed loss, compared to just using a
simple partition instead. Other logical volume abstractions,
either in hardware or software, can drop your performance too.

--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
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