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How many disks to group at one time on EVA

Del_3
Trusted Contributor

How many disks to group at one time on EVA

Can some one point me to official docs stating how many disks you should group on an EVA at once? Many different opions here.

Thanks
11 REPLIES
Steven Clementi
Honored Contributor

Re: How many disks to group at one time on EVA

Del:

The minimum you can group is 8. So at the very least, you can have multiple disk groups with 8 disks apiece.


HP best practice is to place as many disks in 1 group as possible. I have the doc somewhere, but the link is not handy. When I find, I will post, or someone will post.

Some of the reasons for this is because you get better performance when there are more disks handling your data, you also have the highest available disk space with one disk group.

Best practice also says to add disks in increments of 8. This is partly due to how the EVA handles redundancy, which is a whole other conversation. (which we can get into if needed).


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)
Mario_66
Valued Contributor

Re: How many disks to group at one time on EVA

Hi,

see following best practice doc:

http://h200001.www2.hp.com/bc/docs/support/SupportManual/lpg29448/lpg29448.pdf

Page 18.

I have to say that some recommendations seem to me a little bit strange, but on the other hand this is official doc on HP site.

regards,
M.
Uwe Zessin
Honored Contributor

Re: How many disks to group at one time on EVA

> Best practice also says to add disks in increments of 8.

My understanding is that they mean to enhance a disk group by a multiple of 8 disk drives. So if one needs to add capacity to a disk group, one 'should' add, e.g. 16 disks, not 14. In that case I would add all 16 disks to the group, not the first 8 and after leveling the other 8.
.
Steven Clementi
Honored Contributor

Re: How many disks to group at one time on EVA

I agree. As long as it is a multiple of 8 disks, your satisfying the controllers and making their job easier.



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)
Del_3
Trusted Contributor

Re: How many disks to group at one time on EVA

Uwe, can you clarify your statement?
Steven Clementi
Honored Contributor

Re: How many disks to group at one time on EVA

All that is being said is that it is alright to add 16 disks to a group at once. Don't take the "add in increments of 8" as a literal number. It really means as long as you add a multiple of 8 disks...

8 disks
16 disks
24 disks
32 disks
40 disks
etc...

you make the controllers job easier when it comes to allocating RSS groups, which is done transparently by the controllers.

If you had to add 32 disks to a DG, you do NOT have to add 8, wait for it to level, add the next 8, wait for it to level, add the next 8, level, add the final 8 and level. It is ok to add all 32 at once.

Additionally, if you only needed 1.5TB ( 5 300GB disks), you shouldn't just add the 5 disks... you should add 8 disks. A bit more costly, but better in the long run.


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)
Del_3
Trusted Contributor

Re: How many disks to group at one time on EVA

Are you suggesting I can do damage to my RSS config by not adding in groups of eight?
Steven Clementi
Honored Contributor

Re: How many disks to group at one time on EVA

No, just saying that the controllers will have to do some extra work if you add a smaller set of drives to a group.


Assume your DG is 16 Disks big, your RSS groups should be 2 sets of 8. If you add 8 disks, you get a new RSS group of 8.

If you add 4 disks, you will end up with potentially 2 groups of 10 or perhaps 1 group of 8 and 2 groups of 6.


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)
Uwe Zessin
Honored Contributor

Re: How many disks to group at one time on EVA

Well the 'rule of 8' is certainly great for large environments and when the arrays run with unlimited licenses. But, in my opinion, it is unrealistic to expect this from smaller configurations, where one more disk drive might require another 1TB LTU or an unlimited LTU, because the 1TB add-on is no longer cost-effective.

And I have seen those small environments.
No: MSA is not the answer!
.
Bill Mace_1
Occasional Advisor

Re: How many disks to group at one time on EVA

you should also add the disk vertically if you are putting the drives into the shelves. (ordered later add-on drives)or select the drives if they are in already with disk locate. The EVA should pick the drives from different shelves but.....
Timothy Cusson
Valued Contributor

Re: How many disks to group at one time on EVA

A couple toughts...

The best pratice document states that one must find a balance between performance and data availability. For maximum performance, one disk group is better. If you have a data base, you should have two disk groups, one for the data base and one for the log files.

The best pratice for adding disks to an EVA is to insert one disk at a time, wait about one minute, (this time is needed for the EVA to test the disk, give it a disk number, then add it to the "Ungrouped Disk Group"), then add another disk, wait a minute and so on, until you have 8 disks added in a vertical column. You are now ready to add these 8 new disks (from ungrouped disk group) to an existing disk group.