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тАО06-03-2009 03:00 AM
тАО06-03-2009 03:00 AM
EVA Best Practice (RSS, Balancing Loops and drive numbers)
I am wanting to try and put something to bed that has been a burning question in my company for quite some time now - and I finally have the supporting evidence to ask the appropriate questions, and hopefully find the answers.
EVA best practice guide for 4x00/6x00/8x00 states the following:
1) Keep your disk group to a number that is a multiple of 8.
2) Let the EVA choose which disks are to be added into the relevant disk groups.
3) The number of disks per drive enclosure should not differ by more than one.
4) Try to load balance the number of disks within the loops.
Now four EVA's have recently been installed at two separate customers of ours. All have been EVA 8100 2C18D arrays, with 144 disks in one pair, and 200 disks in the other. LetтАЩs discount the fact that the EVA's have room for expansion and imagine that they will never have another disk added.
The first pair of EVA's I spent quite some time balancing the number of disks per loop, drive enclosure and disk group. The second I followed HP's best practice ,and inserted all of the disks prior to initialization and then carved out the disk groups. It should be noted that both arrays have 4 disk groups which are split on the I/O profile and vRaid types.
I have just analysed the results of the SSU capture of both arrays and I find something a bit puzzling. On the arrays where I spent some time balancing everything manually - there are no drives that have shelves in common in the one array and 2 drives that have shelves in common in the other array. However where the EVA was left to decide where the disk groups will be carved out etc the following can be found:
RSS #3 has 4 drives that have shelves in common.
RSS #5 has 4 drives that have shelves in common.
RSS #6 has 4 drives that have shelves in common.
RSS #7 has 4 drives that have shelves in common.
RSS #12 has 4 drives that have shelves in common.
RSS #15 has 6 drives that have shelves in common.
RSS #16 has 6 drives that have shelves in common.
Now home come there is such a difference between the two?
What have the EVA's done differently?
Why is this so?
Should I be worried about it?
Should I leave the EVA's to their own devices every time?
Does anybody have technical reason as for one method versus the other? I am looking for some deep dive technical reasons and not just a "HP says so"
I can provide any RSS maps, warnings etc if anybody would like to see them.
Many Thanks
Andrew
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тАО06-03-2009 04:52 AM
тАО06-03-2009 04:52 AM
Re: EVA Best Practice (RSS, Balancing Loops and drive numbers)
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тАО06-03-2009 07:21 AM
тАО06-03-2009 07:21 AM
Re: EVA Best Practice (RSS, Balancing Loops and drive numbers)
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тАО06-04-2009 03:54 AM
тАО06-04-2009 03:54 AM
Re: EVA Best Practice (RSS, Balancing Loops and drive numbers)
Please find the LS Disk Full for 3 of the arrays. At present I don't have the scans for the fourth on hand. Please ignore the 23 FATA disks in EVA 2 Pair 2, as they are temporarily housed on this EVA until a new array can be procured, and one disk has failed.
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тАО06-04-2009 11:35 AM
тАО06-04-2009 11:35 AM
Re: EVA Best Practice (RSS, Balancing Loops and drive numbers)
Looks like EVA003 made a major screw-up on DG04!! Has the disk group been expanded at one time?
You also have a duplicate disk name (022) in EVA001 at E:01/B:02 + E:18/B:02 and a 'parity state' degration.
EVA002 looks fine.
Reports are attached - enjoy.
Please ignore the "NewFW" column in the disk listing - I have not kept the tables current.
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тАО06-04-2009 11:58 PM
тАО06-04-2009 11:58 PM
Re: EVA Best Practice (RSS, Balancing Loops and drive numbers)
That disk group wasn't expanded funnily enough...I'm debating uninitializing that array again (its been troublesome since I turned it on about a 10 days ago).
Based on your findings do you know why EVA's do this ? and do you have any answers to my questions above ?
PS What application are you working with ? Is that a Navigator report ?
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тАО06-05-2009 12:32 AM
тАО06-05-2009 12:32 AM
Re: EVA Best Practice (RSS, Balancing Loops and drive numbers)
More than 4 years ago I've heard rumors that engineering was thinking about code enhancements to allow 'automatic RSS repairs', but apparently that never happened and even the basic code is far from perfect. Here on the ITRC forums I've read that HP gives no support if somebody attempts to fix it on his own - sorry, I don't have a pointer to the thread. Maybe you can ask HP for an official statement.
The 'application' does not have a name. Well, it is just a set of APIs without a nice user interface. It is based on 9..10 years old code I did to analyze / model HSG-based storage arrays.