[Techtalk] Re: ATA RAID with Promise FastTrack

[Scott Sandeman-Allen (RSCorp)]

> >of SCSI emulation for various devices.
> 
> But I'm trying to do native Linux (hardware) RAID - just want to use the 
> Linux drivers instead of the Promise ones for my controller. Unless I'm 
> getting it all wrong?

Sorry, Promise ATA-RAID is _not_ hardware RAID. No matter how you install, i.e.
with Promise, Linux or BSD drivers it is still SW-RAID.

The [embedded] card is simply a two-channel IDE controller with a different
BIOS and a slight change of hardware (a diode is my understanding).

You will run into boot challenges with the Promise BIOS depending upon how you
do the install too, btw.

> Thanks to Scott too for your answer - not quite what I needed but I 
> appreciate you taking the time.

You are very welcome. However, if you want to use Linux drivers... it _is_ what
you need. I'm no pro, but I've worked with RAID for several years though only
Linux SW RAID for just over a year on half a dozen systems. A fellow I know
here in central Alberta, Maurice Hilarious of Hard Data
(http://www.harddata.com), is extremely knowledgeable and has been a great
resource. Here is one of his comments:

    There is precious little in difference. The "hardware raid"
    drivers are really just branded software RAID. 

    "The biggest difference is that the Linux "software RAID"
    is faster and more robust. It continues to develop with the
    kernel and newer ATA drivers, whereas the Promise drivers
    do not. "

The whole thread I pulled this from re. Promise ATA RAID is at:
    http://www.vmlinuz.ca/archives/elug/2002-02/date.html

Basically there are three options for your hardware (I didin't offer the third
in my first email). Because you have two drives and one is already installed, I
assumed you wished to mirror for security. There are two logical choices for
installing Linux SW RAID to do this. They are:
    A) config during install using RH/'drake installer
        (I prefer to partition with Knoppix & fdisk for beter conrol)
    B) re-configure a running system using raidtab, makeraid etc.
        I have not fully explored the mdadm/raidtools optios for this 

The third option is to install your system on a separate drive (no failure
protection) and add RAID as multiple other dirves like a RAID-5 with hot-spares
and other fancy things. With persistent superblocks, the kernel can auto-detect
what drives are in a particular arary, it just won't auto-mount that array as
/var or /home etc.

So, the predominant opinion I've read through archves etc. (not just Maurice's)
is to not use the Promise drivers as they limit your ability to upgrade your
system in the future.

So, unless you wish to blow your system away and re-install, it looks like
option B would be your best choice. Similar things will have to happen if you
wish to RAID-0 your /var, but RAID-1 your /home with an existing installation.

The articles I couldn't find are at the following link. There is a Part II
linked from this part one.
    <http://www.linuxjournal.com/article.php?sid=5653>

I hope this helps,

Scott