EVA status and set up need serious help

[cheesytime]

This is our current EVA 4400 setup:

Total: 3871 GB
Allocated: 3108 GB
Allocation level: 80 %
Available: 762 GB

We have a total of 22 disks, 12 x 146GB FC 15K + 10 x 300GB FC 15K

The actual level of protection is single meaning we're reserving 2 x 300GB

Available (estimated)
Vraid0: 305 GB
Vraid1: 122 GB
Vraid5: 228 GB

Total: 3871 GB
Allocated: 3108 GB
Allocation level: 80 %

Why the total available for vraid0 is 305GB?

Available shows 762GB with single protection enabled. I cant really get EVA's math methods, bare with me on this one.

What would happen if we loose one disk, worst scenario a 300GB one, would we loose single protection? The reason I'm asking this is cause we have 305GB available for a vraid0 lun that space also would be used to mantain the singles status?

[Uwe Zessin · Accepted solution]

You might have a version of CV-EVA, that can't display the capacities in the disk group properties page properly.
I suggest that you go into the "create a new virtual disk" dialogue and check if you see the same values there.

[cheesytime]

Command View EVA V9.03.00 Build 100811 and the controllers FW is 09534000 I tried to create a vdisk and I see the very same values. Anything else?

[Uwe Zessin]

> What would happen if we loose one disk,
> worst scenario a 300GB one, would we
> loose single protection?

The VDISK's data protection is in the virtual disk's VRAID-1/5/6 level. VRAID-0 has no 'RAID-protection', no matter if you set the disk group's so-called "protection level" to single or double.

> The reason I'm asking this is cause
> we have 305GB available for a vraid0 lun that
> space also would be used to mantain the singles status?

Yes, but...
First, the EVA uses capacity from the free space for virtual disks in order to keep the reservation in the "protection level" as long as possible.

But if you make use of that free space, the "protection level" makes sure that there is enough capacity for a full VRAID-recovery, even if all disks are VRAID-1 (that's why 2times the amout of the largest disk in a disk group is reserved).

[Sheldon Smith]

To summarize: If you lose *any* disk from the disk group, *all* RAID0 LUNs are trashed.
Single or double protection and LUN rebuild *only* work on RAID1, RAID5 and RAID6.

[Víctor Cespón]

When you mix disks of different sizes on a disk group, the space calculations are not straightforward.

Usually:

Vraid 0 space = Total - used = available
Vraid 5 space = (Total - used)*4/5
Vraid 1 space = (Total - used)/2

But when there are disks of different sizes, this is not true and there can be less space available than expected.

The "disk failure protection" = Single reserves 2 x 300 GB as you say, this is already discouted from the Total.

You have 12*137 + (10-2)*279 = 3876 GB, which is close to the total of the disk group.

The 146 GB disks will fill faster than the 300 GB ones, you cannot use all the space on all disks, so the space available for new vdisks is less than (total - used).