topic Re: EVA4400 disk allocation level in HPE EVA Storage

EVA4400 disk allocation level

johnCatBE — Tue, 13 Mar 2012 13:17:29 GMT

EVA4400 disk allocation level

Apologies for empty subject - browser blanked it out!

Can someone give a definitive steer on allocation levels on a disk group of 32 x 450 FC disks, currently at 95% showing

c. 500 Gb of free RAID 5 space.

Question is how much space to leave in situ - need to increase an existing CA'd VDISK by 250 Gb but could make do with 150Gb.

I've read in other posts that only 5GB free space required but also heard many conflicting views on this subject.

Many thanks

John

Re: EVA4400 disk allocation level

Johan Guldmyr — Tue, 13 Mar 2012 18:28:23 GMT

I suppose they are conflicting because they apply to different situations.

Here is some information: http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c00877006

If you have disk drive protection and what level would matter for this steer.

More free space means faster reconstruction and leveling.

If you want them to stay at the same speed as it is now you probably shouldn't decrease the amount of available space.

Re: EVA4400 disk allocation level

johnCatBE — Wed, 14 Mar 2012 13:05:48 GMT

Johann

Many thanks for your prompt on this....i have tried to post a star but not sure if it registered.

I have read the white paper and have difficulty comprehending the distinction between

the comment

"Protection level reserved capacity is not associated with the occupancy alarm setting. These are independent controls."

I'm not clear what this means.

We're using single protection on the group and i've calculated that our present level of 96% is too high. We have 450GB FC disks with a total of 12566 raw... i calculated 92% based on twice the capacity of our 32 x 450 disks (plus 5 GB) using the formula in the "Best Practices" White paper - but i'm a little hazy what this means in terms of the impact of losing disks in the 4400.

Thanks again.

John

Re: EVA4400 disk allocation level

Johan Guldmyr — Wed, 14 Mar 2012 16:04:10 GMT

"Protection level reserved capacity is not associated with the occupancy alarm setting. These are independent controls."

So, the protection level reservs capacity. Occupancy alarm is calculated by Total capacity of the DG that is currently in use by the virtual disks. It is a % calculation by dividing total capacity in use by virtual disks by usable capacity.

Maybe the rest of the % are in use by CA or BC? Are those included in your calculations too?