Re: RAID newbie...can I have several partitions on a RAID 1 array?

Previously Curious George <cg@xxxxxxxxx> wrote:
On 11 Sep 2006 12:14:56 GMT, Arno Wagner <me@xxxxxxxxxxx> wrote:


I don't disagree with Arno at all: as he kinda said, for true
*hardware* redundancy, you need *at least* a spare controller.

"at least" is the key phrase. Adding a second controller and array
means that the host computer is now a single point of failure instead
of the DAS as well. That may be OK but the real goal is redundancy
that is appropriate to the situaion/applicaion. IMHO In a lot of
cases with modern HW the old online second controller concept is a
waste that well exceeds the point of diminishing returns. IMHO it is
more common for either simpler DAS or larger cluster other
multi-computer system to make more sense. YMMV. Of course I'm
talking live HW, not spares. You may disagree but the key is there is
no definitive best protection via redundancy on a small scale- it all
depends.

You did get that we were talking about a cold spare and no second
array was ever mentioned?

But even total hardware redundancy does not supply any protection
against bad software (e.g., Windows) or against funble-fingers.

My conclusion: RAID is nice, but backup is essential.

Indeed. You are entirely correct of course. With current backup
you can do away with the spare controller. I am getting so used to

Often, especially with desktops like the OP has.

But without raid the whole system or volume goes down during a repair
and restore when there is hardware failure/decommission or certain
kinds of storage upgrades. Sometimes that isn't acceptable so the
argument for raid in those cases goes beyond the protection mechanism.

Also there are some RAID implementations that can assist is resisting
data loss/corruption due to failing/marginal media. Backup and manual
intervention does not address that particularly well.

Of course the OP is talking about entry level PC desktop RAID 1.

Indeed. BIOS level at that. See above.

But
there are also theoretical performance benefits in better
implementations as well as some other levels which are used to boost
storage speeds. In those cases, of course. the presence of a current
backup is quite irrelevant to the argument for raid.

people here running without backup, that I start to overlook
the obvious. Thanks for reminding me!

As Bob says, RAID only protects from hardware problems, so it only
fills part of the things a backup does. Essentially RAID is a
''hassle reducer'': It decreases the probability that you need
to restore your backup.

I agree with this point. But I'd add the caveat that entry level
desktop RAID like the OP's is not 100% foolproof automatic protection
against any & every kind of failure or failing media. So your careful
wording which includes "hassle reducer" and "decreases" is quite
appropriate IMO. Perhaps I'd add the word "potential" to "hassle
reducer." But that's me

Well, I personally have experienced hassle reduction from RAID1
and RAID5, so I feel entitled to not add "potential". You are
free to do so of course ;-)

Arno







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