ATA Raid

[Matthias Saou]

Bill Gradwohl wrote :

> Has anyone tested an ATA Raid 1 setup that utilizes the hptraid.o,
> pdcraid.o, or silraid.o modules?
> 
> By testing I mean force a failure and see what happens. 

Yep, I have. Failures were not intentional, though.

> I spun up a copy of Fedora on a TYAN dual P3 mobo that has a Promise
> 20267 chip, applied all the recommended patches via up2date, and insmod'd
> ataraid and pdcraid, formatted and then mounted a partition for testing. 
> 
> I was surprised to find that the Promise controller allowed the O/S to
> find hde and hdf even though I used both identical drives to create a
> single RAID1 array via the Promise BIOS. My Google research suggests that
> all these mobo installed RAID controllers don't provide real hardware
> RAID, but offer a quasi (and I think unreliable) hardware/software
> solution. Is that true?

Possibly. I've installed RHL 7.3 on a bunch of Intel 1U servers which have
those Promise FastTrack ATA RAID controllers integrated, and had nothing
but trouble.
After system crashes (those servers are incredible unreliable for reasons
I've been unable to track down), the arrays on some servers became
completely hosed, and all attempts to get things back to normal failed. I
went as far as going into single user mode and dd'ing directly one drive to
the other using /dev/hdX directly. I knew it was something to avoid, but
that was my last resort and still didn't get things working again.

BTW, I'm still running 2.4.18-x on those servers as I've experienced severe
and systematic data corruption with later 2.4.20-x errata kernels for RHL
7.3. I've still got a bugzilla entry open for that IIRC, and don't know if
later 2.4 kernels from FC1 or 2.6 are any better since I've never had the
chance to test any on that hardware.

My advice is clearly to stay away from all that ATA RAID cr*p when there's
"Promise" written on it. Either just use the second disk for regular or
occasional backups, or use software raid, which is much more reliable in my
experience and very easy to set up and monitor, especially since mdadm came
along.

Matthias

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