Disk Enclosures
cancel
Showing results for 
Search instead for 
Did you mean: 

Does EVA RSS split consider distribution of disks to shelves?

SOLVED
Go to solution
Kurz
Frequent Advisor

Does EVA RSS split consider distribution of disks to shelves?

Hi,

let's assume I have an EVA 6000 disk group with 16 disks evenly distributed to 8 shelves (2 per shelf). Then ideally I have 2 RSS sets with 8 disks. How can I see the RSS sets in the configuration and verify that this is really so?


If then I add 4 disks, then 4 shelves will have 3 disks and 4 shelves will have 2 disks.
One RSS group will split: 12 -> 2 x 6. Will the RSS group split in such a way that the failure of a complete shelf is still accounted for? If the RSS splits up randomly, then the 3 disks might not be in different RSS sets, and a failure of a complete shelf will result in data loss. On the other hand, it would be possible to redistribute the RSS sets in a good way that will cover the problem. Does the EVA do that?

As mentioned above, it would be good to have a way to verify this.

best regards,

Michaela
6 REPLIES
Johan Guldmyr
Honored Contributor
Solution

Re: Does EVA RSS split consider distribution of disks to shelves?

Capture the controller configuration dump. In there you can see which RSS the disk is located on.

In CV 9.x you go to server options -> capture system information.

In the older ones you will have to resort to a command in SSSU - I don't remember which. Also in some older CV you can see which RSS the disk is in from the web interface.

john_347
Regular Advisor

Re: Does EVA RSS split consider distribution of disks to shelves?

HI Michaela,

Best practice state that you add disks in bundles of 8. If you add just 4 you have the potential to start to break down the reslience of the Array. RSS sets comprise of 6-11 disks. We are in the process of restructuring one of our overseas EVA's because best practice wasn't followed. It is a very slow process. The system will be able to work out the correct RSS set config provided you place the new disks in a vertical pattern ie 1 per shelf.

In the older versions of CV you use to get the RSS id in the disk information. From 6 onwards it was taken out by HP becuase it was felt we didn't need to know.

Hope this helps.

regards

jc
Sivaramakrishna_1
Honored Contributor

Re: Does EVA RSS split consider distribution of disks to shelves?

Hi,

Firstly, For EVA6000 disk Enclosure there should be minimum 4 Disks should be in each enclosure. If not EVA will not detect that Enclosure.

Generally When initializing the Array / Creating DG, Controller will try to Assing the RSS vertically. for Eg, if we have 4 Disk in each enclosure and 8 Enclosures, There will be 4 RSS will be created and 4 disk in Each enclosure will be of seperate RSS set. but No body will be guarantee about maintaining the same kind of RSS after RSS split and Merge (Long back i got an update from HP L2)

one imp point raised about "Data Loss" assumption: If one Enclosure Failed in un-uniform RSS Split only Data is unavailable after failure and same will be available if Enclosure Replaced, it should not treat as Data Loss.

Data Loss will only happen if Multiple Disk Failed in Same RSS group at a time.

Kurz
Frequent Advisor

Re: Does EVA RSS split consider distribution of disks to shelves?

Hi Sivaramakrishna,

do you any detailed information on how the controller tries to assign the RSS vertically?

thanks,

Michaela
Steven Clementi
Honored Contributor

Re: Does EVA RSS split consider distribution of disks to shelves?

The RSS process has, for the most part, been kept secretly amoung the HP folks. Not much information has been released about "how" it works out it's magic.

Most of the information has come from experience and experimentation by the customer community.

Theoretically, when the RSS group splits... it should take 2 disks from shelves where you did not put a new disk in. You "should have" something like...

1 3
1 3
1 2
1 2
1 2 3
1 2 3
1 2 3
1 2 3

If you add 2 more disks..

1 3
1 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3

If you add 2 more...

1 3 2
1 3 2
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3

I am guessing on this of course, but the controllers are supposed to be "smart" enough to do this.


Steven
Steven Clementi
HP Master ASE, Storage and Clustering
MCSE (NT 4.0, W2K, W2K3)
VCP (ESX2, Vi3, vSphere4, vSphere5)
RHCE
NPP3 (Nutanix Platform Professional)
DinoC
Occasional Visitor

Re: Does EVA RSS split consider distribution of disks to shelves?

Probably not for everyone but if you're performing Media resource hungry applications then getting this right is crucial.

The above took a bit of tweaking.

 

Cheers

 

DC

Photo Slideshow Creations