SATA Raid

[CLIFFORD ILKAY]

On June 18, 2006 19:09, Dave Cramer wrote:
> On 18-Jun-06, at 1:52 PM, CLIFFORD ILKAY wrote:
> > 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?
>
> Well, I have seen UPS's fail, and I figure my data is worth a whole
> lot more than the cost of a decent RAID card.

As I explained above, I already have decent RAID cards, which I 
disable and subsequently use software RAID because it seems that 
kernel support for even popular cards can change without warning. My 
motivation clearly isn't cost since I already own the cards. Besides, 
I have seen all sorts of batteries fail. What makes the battery 
backup for your RAID card any more reliable than a UPS?
-- 
Regards,

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

+1 416-410-3326
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