Usable Space in EVA

[Sharjeel Saleem]

HI,

Can any1 tell me if we are adding eight 300GB hard disk in different disk group, how much space we getting in usable space?

-Sharjeel

[Patrick Terlisten]

Hello Sharjeel,

are the 8 disks member of a disk group? If yes, you need to ungroup those disks, and create a new DG with that disks.

Let's assume a new disk group with 8 disks and a protection level of "simple". You will get a usable capacity of round about 2,1 TB.

Best regards,
Patrick

[raadek]

Patrick,

Where did you take that number from?

HP StorageWorks Sizing Tool gives following figures:
100% VRAID5 -> 1440 GB usable
100% VRAID1 -> 900 GB usable
(8x 300GB, single protection,95% occupancy)

Rgds.

[Patrick Terlisten]

Oh sorry, the 2,1 TB was only the usable capacity, which can be used to create vdisks.

8 disks x 300 GB - 300 GB (single protection) x 0,95 = 1,995 TB useable capacity.

[raadek]

Still it doesn't stack up - the maximum size of a vDisk you can create is 1440GB for vRAID5, or 1800GB for vRAID0 (which you really shouldn't be using for a production data ;-)

[Uwe Zessin]

> 8 disks x 300 GB - 300 GB (single protection) x 0,95 = 1,995 TB useable capacity.

Assuming to configure a new disk group:
'Single protection' reserves 2x300GB (to be able to recover VRAID-1 data to new mirror pairs. Also, 300GB is the disk size in Hardware GigaBytes
(HWGB = 1,000,000,000) while the EVA displays Software GigaBytes
(SWGB = 1,073,741,824).

(8-2)*300/1.024/1.024/1.024 = 1676.380 SWGB

Subtract 5 to 10 SWGB to give the EVA some room for 'breathing' (5% is a waste in these days - check the latestest best practice guide).

VRAID-0: 1675 SWGB
VRAID-1: 837 SWGB
VRAID-5: 1340 SWGB


Sharjeel's question cannot be answered, because we don't know how the existing disk group is configured (size + number of disks, protection level).

[Patrick Terlisten]

Moah... You're right, Uwe. It slipped my mind - single = double, double = quad.

Best regards,
Patrick

[Sharjeel Saleem]

Hi All,

Thx for valuable comments...but i didnt get HWGB & SWGB concept :(
Secondly the single protection is occupied 2 disk from the disk group then we didnt subtract 2 disk from the given formula,

8 disks x 300 GB - 300 GB (single protection) x 0,95 = 1,995 TB useable capacity.

UWE, there is 1 disk group configured in our EVA with single protection level.

[Uwe Zessin]

> Thx for valuable comments...but i didnt get HWGB & SWGB concept :(

OK, I'll go a bit more in detail:

I'm sure you know the difference between decimal and binary.
We humans usually work with decimal numbers 1, 10, 100
A computer works binary: 1, 2, 4, ... 512, 1024, ...


I have an EVA with "300GB" disk drives. With the Storage System Scripting Utility (SSSU) I can find out how many blocks a disk drive has:
formattedcapacity ..: 585937500

Each block contains 512 bytes:

585,937,500 * 512 = 300,000,000,000


I divide it by 1,000,000,000 (=1000*1000*1000) and get: 300 GigaBytes

That is what is printed on the disk drive, so it is "HardWare GigaBytes (HWGB)".


Command View EVA divides it by 1,073,741,824 (=1024*1024*1024) and gets: 279.39648

which is pretty much what CV-EVA shows: 279.39


So, it is the same amount of data - just show differently, like:
5(10) = 101(2)

[Sharjeel Saleem]

Thx! we can installed 300GB 15K harddisk in EVA4000?