ufs2 / softupdates / ZFS / disk write cache

[Dan Naumov]

---------- Forwarded message ----------
From: Dan Naumov <dan.naumov at gmail.com>
Date: Mon, Jun 22, 2009 at 1:34 AM
Subject: Re: ufs2 / softupdates / ZFS / disk write cache
To: Andrew Snow <andrew at modulus.org>


On Sun, Jun 21, 2009 at 11:52 PM, Andrew Snow <andrew at modulus.org> wrote:
>
> Šimun Mikecin wrote:
>>
>> 21. lip. 2009., u 13:41, Andrew Snow <andrew at modulus.org> napisao:
>>>
>>> Folks who need to maximize safety and can't afford the performance  hit of no write cache need to do what they always have had to do in  the past - buy a controller card with battery-backed cached.
>>
>> Or:
>> B) use SCSI instead of ATA disks
>> C) use UFS+gjournal instead of UFS+SU
>> D) use ZFS instead of UFS+SU
>
>
> All of these solutions still involve disabling of write cache, with a performance hit of varying degrees. (I have tried all of those except gjournal!)

Why would using UFS+gjournal, ZFS or SCSI still involve disabling
write cache? Disabling write cache is only suggested for systems using
UFS + SU on ATA/PATA disks.

This in turn actually raises a new point: Why is UFS + SU still the
default option provided by the sysinstall installation process? A
simple truth is that most FreeBSD users on a modern system are going
to be using SATA disks. Another simple truth is that most new users
are going to go with what the default installation process suggests
and as shown by the benchmark results a few posts back, noone is going
to be disabling the write cache unless they are completely out of
their mind (who on earth is going to accept 2-4 MB/s write speeds from
a modern disk in 2009?).

- Dan Naumov