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RAID question

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Andy Welcomer_1
Occasional Visitor

RAID question

I'm setting up a RAID 1+0 array with 2 36 gig 15K RPM ultra 320 drives. I would like to set up a hot spare however I don't have another one of these drives avalable. Can I use a 36 gig 10K RPM Ultra 3 drive?

Thank you in advance
8 REPLIES
JohnWRuffo
Honored Contributor

Re: RAID question

Yes you can use that drive...

But you should know that if you do, all the drives will spin down and sync to 10K and also opperate at Ultra3 protocol. So you would loose the Ultra320 and 15K advantage.
Enjoy!
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Andy Welcomer_1
Occasional Visitor

Re: RAID question

Thats what I assumed, I just wanted to be sure. Should the Hot spare kick in, when I replace the bad drive, will that drive automatically rebuild as part of the mirror, or would it become the hot spare?
JohnWRuffo
Honored Contributor
Solution

Re: RAID question

No... the original configuration would be restored. The hot spare would be a hot spare again after a successful rebuild.
Enjoy!
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Uwe Zessin
Honored Contributor

Re: RAID question

No, I don't think they will sync down to 10k. Spindle sync is a very complicated thing - vendors won't even support it between disks of their own different product lines.

I haven't seen any indication that any StorageWorks device supports spindle sync - have you? (that's a honest question - not a rethorical one, OK?)

A 15kRPM disk that spins at 10kRPM will have a completely different aerodynamic behavior. I doubt that the head would lift off.


Transfer speed between the controller and the disks is usually negotiated on an individual basis. Some controllers generally run at the speed of the slowest device, but that is not the rule.

Please look for Q7 on this page:
http://h18004.www1.hp.com/products/servers/proliantstorage/sharedstorage/sacluster/msa30/questionsanswers.html#6

Of course an U3(160) controller cannot do U320 speed to a U320 disk - that's what negotiation is for.
.
JohnWRuffo
Honored Contributor

Re: RAID question

Uwe:

I have always questioned that document claiming that each device will communicate at its own protocol when they are on an Ultra320 bus. To me that is incorrect.

The STA Faq clearly says otherwise:
http://www.scsita.org/aboutscsi/ultra320/faq.html
"
7. Is Ultra320 SCSI compatible with prior versions of SCSI?

SCSI devices are always backward compatible. When newer SCSI devices are attached to a system with devices from a previous generation, the newer devices will back down to the maximum operating speed of the older generation when they are talking. When not talking to older devices, the newer devices operate at their normal speeds.
"

If you RAID these drives together, they will talk to eachother at the common protocol (i.e., Ultra3)

As far as the drive spinning down, yeah... I don't think they "physically" spin slower, only that they syncronize at the slower speed.
Enjoy!
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Uwe Zessin
Honored Contributor

Re: RAID question

Isn't that what HP's Q&A says? A newer device (e.g. an U320 initiator) runs at a slower speed when it is talking to an ULTRA2 disk, but when it is talking to a device of it's own generation (e.g. an U320 disk) it is using full speed. Note the "will back down ... when they are talking".

English is not my native language, but I don't read this as: The initiator always runs at the speed of the slowest device.

I know that pre-merger HP controllers had this behaviour, but I have never heard about it from the DEC/Compaq line.


Sorry, but you wrote: "all the drives will spin down and sync to 10K" ;-)
What do you mean when you now write: "only that they syncronize at the slower speed"? We have the media transfer speed that depends on the rotational speed of the disk and we have the bus transfer speed - I don't think they are coupled.
.
JohnWRuffo
Honored Contributor

Re: RAID question

Uwe:

I think we are saying essentially the same thing that the drives will sync at the common protocol (Ultra3) when they are in the same RIAD. If they are individual drives communicating on the same bus, the text says they communicate at their own protocol.

As for synchronization, the drives have to read / write based upon the signals sent from the controller. The slower drive would always be playing catch up to the other drives if they all did not all talk at the same speed.

Sorry, Andy, to use your thread to churn over this tech.
I am glad to have this conversation though with you Uwe. I always learn buy reading your posts!
Enjoy!
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Prashant (I am Back)
Honored Contributor

Re: RAID question

Hi,

Well Where as as per origial question we can use same. on same array. And driver will work on their individual speeds also. Even they are in single array.

Only thing in my mind is there any way to confirm the same option on same.

Regards,
Prashant S.
Nothing is impossible