Diskgroup Size not correct?

[IvanForceville]

Running EVA4400 with
32x 146GB 15KFC
8x 1TB FATA

Concerning the 8x 1TB FATA we see a total diskgroup capacity of 5586 GB.

I would expect about ~7,5TB as calculated when you use the Storageworks Sizing tool.

[Schwarzie]

Hi Ivan,

What is the Disk Drive Failure Protection Level you have set on this disc group?

The greater the level of protection (ie Double)the more space is used.

Cheers
James

[IvanForceville]

Protection level = Single

Screenshot in attachment... still 5586GB is still a strange number compared to 8TB of diskspace, even taking the protection level into account.

[Schwarzie]

Yeah I know what you mean. Command View is showing the correct amount though.

If you look at Disk 011 for example from you disk group, you will see even though the drive is 1tb the formatted capacity will actually be lower then that.

If you were to have no protection level at all you would still only have around 7.4tb available as the EVA has eaten up the rest for Meta data etc. Add single level sparing and thats another 1.8tb off.

I would say your Command View is showing the correct amount but have another play with the StorageWorks sizing tool and let me know what you find.

Cheers

[Marcus Schack]

Hello Ivan...
Just to clarify the DISK GROUP SPARING level works out like this. If you choose SPARING LEVEL 1 that means the EVA will set aside TWO times the amount of the largest disk size in the group. If you pick SPARING LEVEL 2 you set aside four times the amount of the largest disk size in the group.

[Rob Leadbeater · Accepted solution]

Hi,

The capacity you see is right for 8 x 1TB drives with single sparing.

Single sparing reserves space for 2 x the largest drive in the group, so in your case you're now down to 6 x 1TB.

Disks are sold with sizes in decimal, whereas the EVA displays sizes in binary so:

1TB = 1000^4 Bytes
1TiB = 1024^4 Bytes

(1000^4) / (1024^4) = 0.9095

6 x 0.9095 = 5.4569 TiB = 5587 GiB

http://en.wikipedia.org/wiki/Gigabyte
http://en.wikipedia.org/wiki/Terabyte

Hope this helps,

Regards,

Rob

[IvanForceville]

Rob,

You hit the spot! All credits to you.

Close Case