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тАО01-23-2007 04:48 AM
тАО01-23-2007 04:48 AM
DL380G4 RAID 1+0: Really?
What gives? Any comments?
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тАО01-23-2007 06:14 AM
тАО01-23-2007 06:14 AM
Re: DL380G4 RAID 1+0: Really?
RAID 1 is mirrored across 2 or more pairs of disks for redundancy.
RAID 1+0 is mirrored and striped which provides for performance advantages (i.e. a sequential read of more than 1 track means that alternatively each drive provides it, raising the utilization of the SCSI bus)
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тАО01-23-2007 06:22 AM
тАО01-23-2007 06:22 AM
Re: DL380G4 RAID 1+0: Really?
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тАО01-24-2007 01:13 AM
тАО01-24-2007 01:13 AM
Re: DL380G4 RAID 1+0: Really?
What I really wanted to know was not a textbook explanation of RAID levels but why HP considers it ok to describe and label an array of 2 SCSI disks "RAID 1+0" when this is in fact not possible. Two disks can either be RAID0 or RAID1; 4 disks are required to reach RAID 1+0.
I'm sure HP knows RAID levels quite well but they've been doing this for years re two disks. They don't call it RAID1 or RAID0 like Dell and other server OEMs do. The question then is, are they just using the term improperly or is there some sort of technology in play that HP thinks they can use the term RAID1+0 to describe two disks and what they can do with them? If not, they really shouldn't be using the term in this manner as it's confusing and misrepresenting acutal RAID levels.
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тАО01-24-2007 01:29 AM
тАО01-24-2007 01:29 AM
Re: DL380G4 RAID 1+0: Really?
If you read David's reply again, I think he has already answered the question...
To put it another way (if I've understood correctly) with RAID 1 there are two disks. All of the I/O will occur on one of these, with the second drive being just a mirror.
With RAID 1+0 with two disks, read I/O could come from either disk, thus giving better performance.
That sounds right, but feel free to correct me...
Cheers,
Rob
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тАО01-25-2007 03:16 AM
тАО01-25-2007 03:16 AM
Re: DL380G4 RAID 1+0: Really?
However, if I present this to my coworkers, I'm not certain they're going to believe it.
Is there any technically meaty paper that explains how this works? I'd be quite interested to read up on it.
Thanks you all for answering my questions!
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тАО01-25-2007 03:41 AM
тАО01-25-2007 03:41 AM
Re: DL380G4 RAID 1+0: Really?
PDMeat, the fact that HP Array Controllers states that even with two drives it is RAID 1+0 is just some kind of simplification done by HP. But after all they could just call it "RAID 1/RAID 1+0.
Here is HP summary of RAID methods:
http://docs.hp.com/en/J6369-90036/ch01s04.html?jumpid=reg_R1002_USEN
And here is a bit more technical document (look at table one):
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00386950/c00386950.pdf?jumpid=reg_R1002_USEN
I hope this will help you to convince your coworkwers.
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тАО01-25-2007 03:46 AM
тАО01-25-2007 03:46 AM
Re: DL380G4 RAID 1+0: Really?
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тАО01-25-2007 03:55 AM
тАО01-25-2007 03:55 AM
Re: DL380G4 RAID 1+0: Really?
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00386950/c00386950.pdf
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тАО01-25-2007 04:07 AM
тАО01-25-2007 04:07 AM
Re: DL380G4 RAID 1+0: Really?
In both cases ADU showed:
Logical Drive 1:
Fault Tolerance Mode: Mirroring