Missing available space after expanding.

[Tdrelichowski]

Hello there,

We have almost run out of space on one of our disk group on EVA 4000 and we had to expand this disk group by 4 piece of 300GB.  That DG had 72GBx8 –72GBx2 (disk drive failure protection level – single)= 409GB and we would have so much space if we choose raid0, but mostly we choice raid5 and have a little less space and it is obvious. Few days ago we expanded this group by 4 piece of  300GB and now we have:

72GB*8+300GB*4-300GB*2(disk drive failure protection level – single) = 1104GB as it should be. The strange thing is we can use only 422GB in vraid0 after expanding. We have lost 280GB somewhere. In my calculations it should be about 702GB in vraid0.

I have to admit that this situation surprised me.

Can anybody tell me how is this happened? What did I miss?

Ps We have unlimited space license.

[Tdrelichowski]

In extension of my first message I'm sending attachment from Command View. In other Disk groups the sum fields Total Occupancy and Maximum Vdisk size Vraid0 is equal or very similar to Total Capacity, but on this disk group is missing 279GB why? 

[Johan Guldmyr]

Hi, without even thinking about the math behind this. If you want to do the math one way might be to capture the configuration dump and then do a manual calculation of the disk space. // edit: But on the other hand, from when I've checked this if it's wrong in CV it's usually wrong in the configuration dump too..

I've seen this total capacity etc being reported wrongly in some XCS and CV version combinations before 6.240 and CV 9.4.

[Tdrelichowski]

Hi,

I'm afraid there is something wrong with RSS (Redundant Storage Sets) and different HDD sizes in this disk group (8*72 and 4*300). I didn't mention earlier but look at previous attachment from CV I'm able to create a Vdisk bigger in raid1 than in raid5.

[Johan Guldmyr]

Hi, I'd say that's normal when you mix 72GB and 300GB disks in the same DG.

However I do not off-hand know the math / the reason behind it.

I believe the recommendation is to have the same disk sizes and speed in the disk group to uilize the disks most efficiently.

[Tdrelichowski]

I know it isn't recommended, but it is a best practice

Best practice to minimize the cost of storage: Mix disk sizes within a single Disk Group.*

Source:
HP StorageWorks Enterprise Virtual Array configuration best practices

 On the other hand only those disks were available to buy and compatible with our EVA.

If someone can do the math, i will be appreciated.