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# Calculating occupancy alarms on HP 8400 EVA

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Occasional Contributor

## Calculating occupancy alarms on HP 8400 EVA

Hi all,

We are having a bit of difficulty calculating the occupancy alarm for a HP 8400 EVA. From the HP EVA best practices guide, we use the forumla:

Occupancy_Alarm = 100 – ceiling { [ max ( PDM_capacity, HP Continuous Access_log_sum) + 5GB / total_disk-group_raw_capacity ] }

For example, one of our disk groups has 80 x 300GB disks with a failure protection set to double. Can someone please confirm if I am using this forumla correctly as below:

PDM Capacity = 4 * disk size = 1200GB
HP Continuous Access_log_sum = 4209GB
total_disk-group_raw_capacity = 80 x 300 = 24000GB
Formatted capacity reported by EVA = 21228GB

Therefore:
Occupancy_Alarm = 100 – ceiling { [ 4209 + 5GB / 24000 ] }

= 100 – ceiling { .1755833333 }
= 100 - 18
= 82%

Can someone confirm if these workings are correct as having the alarm set at 82% seems to be pretty low.

2 REPLIES 2
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Honored Contributor

## Re: Calculating occupancy alarms on HP 8400 EVA

Actually it would be 80% because you must use the real capacity of the disks (279 GB). Then, if you want to make sure you have free space enough to allow the DR logs to reach maximum capacity before being invalidated, you must reserve 4209 GB (20% of the disk group).

You can also lower the disk failure protection to single (with 80 disks double is not justified), or reserve less space for the DR group logs (it's unlikely that all DRgroup logs fill to the maximum at the same time).
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Occasional Contributor

## Re: Calculating occupancy alarms on HP 8400 EVA

Thanks for the clarification. Much appreciated.