SATA Raid

[CLIFFORD ILKAY]

On June 17, 2006 23:50, Dave Cramer wrote:
> On 17-Jun-06, at 8:06 PM, Robin Humble wrote:
> > On Fri, Jun 16, 2006 at 08:51:45PM -0400, Dave Cramer wrote:
> >> The areca cards are quite good
> >
> > are they faster than software raid5?
>
> Well, there are other things besides speed. Hotswapping, battery
> backup, write cache, etc

A counterpoint: hardware RAID is too dependent on your hardware being 
supported by the specific version of the kernel module. The MegaRAID 
fiasco is a good example. I have two servers that have MegaRAID SCSI 
controllers which were both running pre 2.6.9 kernels. I had added 
some new drives to the machines and had reconfigured the RAID volumes 
thus (knowingly) blowing away all the data on the drives. I figured I 
might as well install a modern distro. Imagine my surprise to find 
that my previously well-supported RAID controller was no longer 
automatically detected. I tried various distros thinking that the 
packagers of first one I tried might have screwed things up but none 
I tried, other than distros running pre 2.6.9 kernels, detected any 
volumes. A bit of digging and I found that for some reason, the 
megaraid modules had been renamed and were no longer included, if 
memory serves. We're not talking about some exotic or ancient 
technology that could be deprecated without having much of an impact. 
We're talking about one of the more popular SCSI RAID controllers on 
the market. Fortunately, I had no data riding on this.

During the course of searching for answers, I found some convincing 
arguments as to why hardware RAID was potentially dangerous so I've 
been happily using software RAID since. Performance? Don't know, 
don't care. It's "fast enough" but I am reasonably sure now that a 
kernel upgrade isn't going to render my machine unusable.

> I've heard that software raid was fast, or faster, but I still use
> hardware raid cards, for the above reasons.
>
> The larger areca card has optional 1G write cache. With the Battery
> Backup it's not cheap, but then neither is my data

Why is a battery backup for the RAID controller necessary if you have 
a good UPS and automated shutdown facility?
-- 
Regards,

Clifford Ilkay
Dinamis Corporation
3266 Yonge Street, Suite 1419
Toronto, ON
Canada  M4N 3P6

+1 416-410-3326
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