topic Re: Usable capacity on EVA5000 in Disk Enclosures

Usable capacity on EVA5000

L. B. Andersen — Wed, 15 Oct 2003 08:49:13 GMT

Can anybody out there explain to me how I calculate server usable capacity (Raid-5) on an EVA 5000.

Situation is:

32* 73 GB drives
2 Vraid pools
Highest level Hot Sparing

If it makes any difference, snap vill be used in both pools.

Thanks in advance

Re: Usable capacity on EVA5000

Joshua Scott — Wed, 15 Oct 2003 10:36:57 GMT

The way RAID-5 works is that there's a data stripe that goes across all but one of the disks and a parity check on the other disk. So the way to calculate it is:

([number of drives in RAID group] -1) * [size of drives] - ([number of drives used for hot-spares] * [size of drives] = [capacity of RAID group]

HTH

-Josh

Re: Usable capacity on EVA5000

Mike Naime — Wed, 15 Oct 2003 10:42:12 GMT

Plus, you have a Occupancy Level that you do not want to go over.Compaq/HP recommends that you leave at least 10% of the usable total storage space as free space. (No more than 90% occupancy). This allows the EVA to re-shuffle the data when you do have a drive failure.

Re: Usable capacity on EVA5000

Claudiu Schmidt — Thu, 16 Oct 2003 00:40:46 GMT

Hi,

we have a EVA installed with 64*73GB disks, and we have a usable space of 3.2 TB in Raid 5. We have a single disk failure protection. So here is how I calculate usable space. if you have 32 disks, and 2 diskgroups with double protection, you loose 8 disks, 4 on every diskgroup. the raid 5 is a virtual one, but you loose around 20-25% for parrity. so in you' re case, you will probably have a usable space of ((32-8)*73GB)*75% = 1.3 TB

Rgds,

Re: Usable capacity on EVA5000

L. B. Andersen — Thu, 16 Oct 2003 05:32:37 GMT

Thanks a lot Claudiu.

This seems to match my reality qiute well.

Do you, by any chance, know if any official formula or tool exists to do this calculation for various scenarioes ??

rgds

Re: Usable capacity on EVA5000

Claudiu Schmidt — Thu, 16 Oct 2003 05:58:09 GMT

Hi,

i know there is a tools to calculate the usable space, but i never had it. you should ask a sales guy from HP , because they work a lot with this tool.

Rgds,

Claudiu

Re: Usable capacity on EVA5000

L. B. Andersen — Mon, 22 Nov 2004 15:36:30 GMT

Downloaded EVA calculator from this web site