Re: URGENT: Need help rebuilding iir RAID5 array with failed drive

On Sun, Jun 29, 2008 at 11:09:45AM -0500, Sean C. Farley wrote:
> On Sun, 29 Jun 2008, Rainer Duffner wrote:
> 
> *snip*
> 
> > On our HP DL320G5s, FreeBSD7 didn't even detect the MatrixRAID array
> > (RAID1).  Even the Windoze-guys tell us that they don't trust it.
> >
> > So we settled for RAID1 via gmirror.
> >
> > MatrixRAID is a scam, if you ask me - like all the other BIOS-RAIDs we
> > have had the displeasure to see over the years.
> 
> I have been using the Intel MatrixRAID (ICH9R) with RAID1 successfully.
> Already, I have had to replace one drive, and the rebuild worked.  The
> only reason I used it instead of gmirror, which I use on another system
> (FreeBSD-only), is that it allows the whole drive to be mirrored
> regardless of what other OS's I have installed.
> 
> What other inexpensive (cheap! :)) and reliable (assuming MatrixRAID
> counts) whole-disk (SATA) mirroring solutions exist?  The cheapest I
> found on NewEgg is Syba ($12).  Personally, I have never heard of the
> brand.  Is what you can get in the $12-30 range any better than
> MatrixRAID?  Would they be any faster?

The really cheap stuff will not be any better than MatrixRAID - most of them
will be worse.

All the cheap RAID solutions (which includes just about all of them that are
included on motherboards as well as standalone cards) is just software RAID,
where the OS and the CPU has to do all the real work.  The only thing they
provide over a standard non-RAID controller is that they have a BIOS that
understands the RAID format and thus allows you to boot from a RAID volume
(and sometimes can rebuild it from within the BIOS.)
(For simple mirroring it is not even necessary that the BIOS understands the
metadata on the disk to boot from it since both disks are identical and
can be used as a normal stand-alone bootdisk.)

As for speed and reliability there is no real difference between the
different controllers as far as RAID is concerned, since once the OS has
started running they are really just standard harddisk controllers.

(There are some differences between the controller chips used on different
controllers, but most manufacturers don't tell you which chips they are
using, so you will have to look at the card to find that out. (Most of the
really cheap cards use chips from Silicon Image, which does not have the
best reputation in the world for quality.)) 


When using FreeBSD the ataraid(4) driver understands the metadata used
by several of the firmware-based RAID implementations and is what you will
have to use if you want to use one of those formats.
As has been noted several times it does not support RAID5 though, so
if you want that you will have some other solution.


One big disadvantage of using any RAID-card (software or hardware-based)
is that the metadata on the disks are specific to that brand of controllers.
If you move the disks to some other controller it will probably not
recognize them as a RAID-array and you will be forced to reinstall from
backups.
For hardware-based RAID controllers this disadvantage is usually more than
offset by extra performance and (especially for the good cards with
battery-backed chaches) extra reliability.  Such cards are rarely cheap
though.







-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013_at_student.uu.se