# Creating RAID1 on Intel S5520HCR(S5520HC)



## WaterGhost (Oct 20, 2010)

I've got Intel S5520HCR(S5520HC) motherboard with two HDD's (Western Digital RE4 2003FYYS 2.0TB). 

There is integrated RAID controller in this motherboard which allows to create RAD's 0,1,10 levels. I need to create RAID1 and install on it FreeBSD 8.1. 

I have turn off fast boot in BIOS and changed SATA Controller to "SW RAID". Then I restarted server and pressed <CTRL>+<E> to enter IntelÂ® Embedded Server RAID Technology II. 

There I created RAID1. Then I restarted server (there was line something like this during loading: "RAID1 Online"). Then I started to install FreeBSD and it shows that there are 2 disks found and no RAID1 =( 

I really can't understand if this motherboard allows to create fully hardware RAID1 or I need to install some driver to let my newly created RAID1 work? Or it will be easier to create software RAID1 in FreeBSD? 

Thanks to all.


----------



## phoenix (Oct 20, 2010)

Don't use the RAID "hardware" on this motherboard.  It's not actually hardware RAID, it's pseudo-RAID.  The controller just adds a little bit of metadata to the harddrives saying they are part of a RAID-1 mirror.  However, they still show up as individual drives to the OS.  You have to install the ataraid(4) driver, which will then create the *arrX* device.  All RAID processing is done by the OS, on the host CPU, the controller isn't involved.    Since the OS and the host CPU are doing all the work anyway, may as well use software RAID.

You are *much* better off disabling all the RAID features in the BIOS, and using software RAID like gmirror(8).  It will make the drives portable between any FreeBSD system (compared to the pseudo-RAID that will only work on that model of motherboard).

If you configure the BIOS to use AHCI mode, you'll also get better performance out of the controller.  If you do that, ataraid support is also removed.    Yet another reason to use gmirror instead.

Just don't use pseudo-RAID.  Period.    Stick to full software RAID or full hardware RAID.


----------



## danbi (Oct 21, 2010)

The idea of this pseudo-RAID is that it is in fact purely software RAID, but... each 'raid' controller understands and supports different RAID metadata on the drives. Disks with such metadata can be seen by the BIOS as single (RAID) volume and the BIOS would eventually boot from these. This is the only significant difference and one of the benefits from the pseudo-RAID. The other benefit is, that some BIOS-es are able to create volumes, replace drives etc. Some don't.

The downside, as phoenix mentioned is that your RAID array is bound to specific controller architecture (see man ataraid for examples). In my opinion the only safe usage of pseudo-RAID is mirroring two disks. If one disk fails, or if you need to migrate to different controller, chances are you still can access the disk the way it's seen by FreeBSD.

I have had few nasty cases of motherboard (I guess) related corruption of such pseudo-RAID, where one of the drives 'failed' -- that is, the pseudo-RAID controller didn't want to talk to it properly, and the only rescue was to remove the RAID by complicated series of tricks -- strange things happened when I moved the drives to different ports -- hey would work for a while on new ports, then fail the RAID again. After 'spending' all 6 ports, I had the motherboard replaced and never though of that RAID mode anymore 

I believe the performance of some such controllers is worse, when 'RAID' is enabled.

It's very dangerous to use such 'raid' with more than two drives. You are better with the GEOM RAID variants, or ZFS.


----------



## WaterGhost (Oct 21, 2010)

Thanks for the tips to all. I think, I will create fully software raid1 by using gmirror(8) instead of this "pseudo raid" integrated into montherboard. Now I really understand how it works. Thanks to all


----------

