SI SATA Raid

Aleksandar Milivojevic amilivojevic at pbl.ca
Tue Nov 23 22:05:59 UTC 2004


Rob wrote:
> I just installed FC3 and it detects my SI SATA controller and drives
> but it does not see the Raid0 set I have created (4x160GB), it just
> see four individual drives. ANy suggestions? Is this even supported?

I'm not 100% sure (more around 10% sure) about this (not much experience 
with SATA).  But from what I saw so far, SATA RAID built into the 
chipsets for standard PC motherboards usually means "software raid that 
you can define from BIOS".  OS sees those drives separately, and needs 
special set of drivers.  When you have drivers installed individual 
disks are hidden from you, and you only see RAID devices.  RAID is 
handled by the driver (sofware RAID), not by the hardware.  If you 
turned off that RAID support in BIOS, and simply build RAID devices 
using mdadm, you would end up with basically the same thing.  Former by 
using special unstable and still under development drivers, later by 
using standard and stable Linux md drivers.

The only two real differences I see are:

1.  You don't need special drivers if you turn RAID support off in BIOS. 
  This is an argument towards not using chipset/BIOS RAID support, and 
using normal Linux software RAID tools (mdadm).  MD drivers are very 
stable, and easy to use.  Definetly argument for going this route.

2.  If you have more than one OS installed (say Windows and Linux), and 
you want to have Windows partition on RAID kind of device, and you want 
it to be visible from Linux, going BIOS way is the only way you can go.

Said that, I also found that device mapper with help of some additional 
packages might be able to handle those software RAIDs defined from BIOS. 
  Seems to be chipset dependent (not all chipsets supported).  Last time 
I checked, support was read-only.  In other words, whatever changes in 
status of RAID device was detected by the OS, they don't get recorded 
into RAID configuration (for example, if one disk in RAID-1 goes south 
and is totally out of sync).  Next time you boot, your OS dosn't know 
anything about it.  I wouldn't call this actually usable.

-- 
Aleksandar Milivojevic <amilivojevic at pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7




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