On Aug 9, 2005, at 3:51 PM, John A Meinel wrote:
Dan Harris wrote:
On Aug 10, 2005, at 12:49 AM, Steve Poe wrote:
Dan,
Do you mean you did RAID 1 + 0 (RAID 10) or RAID 0 + 1? Just a
clarification, since RAID 0 is still a single-point of failure
even if
RAID1 is on top of RAID0.
Well, you tell me if I stated incorrectly. There are two raid
enclosures with 7 drives in each. Each is on its own bus on a
dual- channel controller. Each box has a stripe across its drives
and the enclosures are mirrors of each other. I understand the
controller could be a single point of failure, but I'm not sure I
understand your concern about the RAID structure itself.
In this configuration, if you have a drive fail on both
controllers, the entire RAID dies. Lets label them A1-7, B1-7,
because you stripe within a set, if a single one of A dies, and a
single one of B dies, you have lost your entire mirror.
The correct way of doing it, is to have A1 be a mirror of B1, and
then stripe above that. Since you are using 2 7-disk enclosures,
I'm not sure how you can do it well, since it is not an even number
of disks. Though if you are using software RAID, there should be no
problem.
The difference is that in this scenario, *all* of the A drives can
die, and you haven't lost any data. The only thing you can't lose
is a matched pair (eg losing both A1 and B1 will cause complete
data loss)
I believe the correct notation for this last form is RAID 1 + 0
(RAID10) since you have a set of RAID1 drives, with a RAID0 on-top
of them.
I have read up on the difference now. I don't understand why it's a
"single point of failure". Technically any array could be a "single
point" depending on your level of abstraction. In retrospect, I
probably should have gone 8 drives in each and used RAID 10 instead
for the better fault-tolerance, but it's online now and will require
some planning to see if I want to reconfigure that in the future. I
wish HP's engineer would have promoted that method instead of 0+1..
-Dan
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