# Disk capacity on EVA 4400

Hello,

I have actually a HP EVA4400 Disk Storage.
The situation is the following :

- I have 11 * 450GB disk (419GB formatted) = 4609GB in 1 Disk Group in Single mode.
- I use 2820GB with VDisk in Vraid5
- It stays only 100GB Free in Vraid5

How is it possible ? I loose 1800GB it's awesome (40% loss)

This is what I think :

- Total capacity : 11 * 419 = 4 609GB
- EVA4400 keep 2 disk (1 per 8 disk)
- (11-2) * 419 = 3 770GB
- I use Vraid5 for each Vdisk : 3770*(25/100)= 940GB
3770-940=2830GB
- 2830-2820(used)=10GB not 100GB which is still free ......

The reflexion is exact or not. How works the disk repartition on EVA4400 ??
How works the disk keeping  (2for8) for levelling or other things and Vraid5 ??????
What implicate the Disk Group in Single mode ???

Thanks in advance for your help, because I need to know how calculate the efficace capacity I will really have to know how many disk buy for my second disk group with 16 disk (then 2 disk keeping also ??)
Thanks to answer to all my questions ...
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Commented:
Sparing level of 1 means you lose 2 disks worth of capacity for the virtual spares (protection level), then after that vRAID5 assignes 4D+P.

So you start with (11-2)*419 = 3771GB available, 4/5 of that is 3016GB, then take off 10% reserve = 2715GB.
(you've got a bit more than that as it doesn't reserve quite a whole pair of disks capacity for protection level of 1 with vRAID5)

Official calculator is SWD Sizer www.hp.com/go/nsssizer

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Author Commented:
What is the 10% reserve you mean ?

I don't understand why we put "protection level" to SINGLE mode then EVA keep 2 disks in order to make levelling when we have a disk failure.

And after there is also Vraid5 protection ...... it's redondant ??? What give more the Vraid5 protection in front of "level protection" to SINGLE.

With SINGLE MODE I'm protected from 1 disk crashed without Vraid5...

Or I didn't understand how it works. Because I loose 2To of data with the both protection.
And did my calcul exact in my first post or not ???
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Commented:
Ignore the 10% I mentioned, it's just the occupancy alarm. This space is reserved for snapshots, if you don't want to use snapshots you can change it to 95%

Protection level is like hot spares on other systems, although in this it doesn't actually take up physical disks but space is reserved across all the spindles.

vRaid5 is normal RAID with parity, if one of the disks in the vRAID 5 group fails it is replaced by a "spare" so that you still have redundancy if a disk fails. You could set the protection level to zero, you'd still have vRAID5 redundancy but if a disk failed you would have no redundancy until it was replaced.

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Author Commented:
OK, if I good understood, the both disks used by EVA for level protection 1 are keeped to assure the direct and immediate redundancy when a disk failed. With vRaid5 and 2 spare disk, a crash failure is transparent. The EVA System rebuild the storage with the spare disk, we don't need to wait to insert a new disk. The data are always reachable with the both protection.

It's that ?
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Commented:
Yes, that's right. With protection level 1 spare space is reserved on the disks so that if a disk fails it can quickly rebuild the contents of that disk onto the remaining spindles to ensure that redundancy is quickly restored before waiting for a person to replace the failed disk.
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Commented:
I wrote one of the early and one of the most accurate EVA calculators (My opinion)
Disk Group capacity
=IF(F25>=4,((F25-(2*H25))*(N25*476))/538,0)
F25 = Number of Disks
H25 = Sparing level
N25 = Useable capacity of Disk
I really cannot remember what the 476 and 538 are all about (Andy do you know?) I spent months in dialogue with the EVA Architects getting this right.
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Author Commented:
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Commented:
By the way, you should normally add your new disks to the existing disk group and create the new LUN on that rather than making a new disk group, that way you don't lose the 2 disk capacity for sparing level of 1 twice. The EVA is designed to have all the disks in just one disk group.
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Author Commented:
OK, thanks, but I think I will need to create a new DiskGroup because the new disk are 600GB, whereas the older are 300 and 450.

One 300 diskgroup, one 450 diskgroup and soon one 600 diskgroup.
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Commented:
In that case probably best to have seperate disk group although with EVA you can mix sizes. Larger ones end up as "hot" disks though as more I/Os likely to occur on them. It's not like your traditional RAID 5 where you only get the capacity of the smallest disks, if you mix sizes it does use the full capacity of the larger ones.
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