Problem with sata2 and raid1.

[Peter Boy]

Am Samstag, den 12.04.2008, 15:42 +0200 schrieb Erik P. Olsen:
> I have installed two sata 2 drives - each 250 GB - which I want to use in a 
> raid1 configuration. My mobo - MSI K8T Neo2 - does not support those sata 
> drives, so I have therefore installed a RocketRaid 1720 PCI-card to get the 
> necessary hardware support.

As to my knowledge the 1720 is not a real hardware raid controller but a
fake raid, i.e. the controllers firmware provides some software to do
some limited raid management, but all the real work is done by your
computers hardware via kernel drivers.

> I have therefore decided to switch to the software available with Fedora and 
> would like to know if the data already located on the disks is accessible to the 
> Fedora driver or if I have to reformat the drives and install all the enchilada 
> from the beginning? 

There is a chance that both use a standard format to manage the raid
disks, so your data may be readable. If you have a full backup you
should just try.

> Luckily I have back-up of everything and can recreate all 
> data it just takes more time. Another even more important question is will 
> Fedora drive the disks through the RocketRaid controller or should I get 
> different hardware and if so which?

In both cases you drive the disks through the 1720. If you use dmraid,
the controllers bios is used for some operations. I you use md, you
disable the controllers bias and just use the SATA connectors and drive
access logik. 

In terms of performance: it's equal. read is the same as if you had a
single disk, write doubles the time needed to write to the disks
(because write operations will be performened twice, one operation for
each disk).

In terms of administration: md does not use propriarity firmware
drivers. In case of a failure or other problem it is easier to check and
handle the disks.

As a general advice: you have to use dmraid/controllers firmware if you
need to share the drives with windows OS, otherwise you should use md.

IT you need better performance you should buy a real hardware raid.
Highpoint RocketRaid 3120 is a cheap one with solid linux support, or
areca ARC1200 (a little bit more expensive). Areca has an excellent
linux driver and installation support, but can not operate with some WDC
Raptor disks (10.000 Upm).


Peter