SAN EVA help needed

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Occasional Advisor

SAN EVA help needed

Just have a few questions on how to work out available capacity and some questions regarding LUNs and disks.

We have 28 x 300GB Online Disks and 8 x 500GB Near Online Disks.

For the Near Online Disk Group of 8 disks, the total capacity is 2793.31GB with single protection. So if the theoretical total is 4TB minus 500 GB, how does it get to 2.8 TB from 3.5 TB?

Also, we presented 2 x 1.5 TB LUNs to a 2008 file server using the Online Disks. We have them GPT, dynamic and spanned so we were left with a singe partition of 3 TB. Is this the best way to do it performance-wise?

Trusted Contributor

Re: SAN EVA help needed

Hi Stix,

500GB size based on consideration of 1000Bytes = 1KB, Hence to get actual formatted capacity of 500GB, you need multiply by (1000/1024) three times, so it comes up to 465.66GB. Now for Single protection you will loose two drives capacity in order to support highest Raid Level(Mirror), so you are left with 6 drives, i. e. 6 X 465.66GB = 2793GB

Regarding spanning to a singe partition , it may be good idea, if Operating System recommends this, but from underlying EVA perspective, it really does not create much difference, because for any LUN, EVA Controller involves all the physical drives for processing IO.

Frequent Advisor

Re: SAN EVA help needed

The actual size of the disks formatted is 465.66GB, so your figure of 2793.31GB is 6 x 465.66GB. You have single disk disk level protection, so that's 1 disk accounted for. From what I can recall, the first disk group holds the quorum or meta data I think, maybe thats your other disk. Saying that I though the first disk group should be FC and not near-line.
Performance wise it depends on what data will be running on the volume, what resilience you require & what the budget is.
Not sure if spanning 2 LUNs is the best way to go with vDsisk. How is it being spanned, via Windows 2008 (software RAID0)?
In the end...
Occasional Advisor

Re: SAN EVA help needed

Thanks for the help!

We have a EVA 4100 so we have a 2TB LUN limit. We needed a partition of about 3 TB for data but we didn't want to create two partitions as we didn't want to shrink one of the partitions if needed.

While I think of it, does shrinking a LUN keep all of the data intact assuming there's enough free space to shrink it?

So, we created a spanned volume. It doesn't use software RAID0 as that is a striped volume. IIRC, a spanned volume simply joins two logical drives into one partition, so performance-wise from the OS side, we should be fine.
Sheldon Smith

Re: SAN EVA help needed

"While I think of it, does shrinking a LUN keep all of the data intact assuming there's enough free space to shrink it?"

Yes. The process is the reverse of extending a partition. First, use 2008 DISKPART to "shrink" the partition. Then have Command View reduce the vdisk. Be VERY careful not to enter a size >smaller< than the shrunken partition.

Note: While I am an HPE Employee, all of my comments (whether noted or not), are my own and are not any official representation of the company

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