HPE EVA Storage

Overhead on FATA 1GB Disks

Occasional Advisor

Overhead on FATA 1GB Disks

We have a new EVA8100 with 24 x 1Tb FATA disks. The disks are distributed over 6 shelves. I have been creating Vdisks today totalling 16Tb. When I went to create the last disk of 1Tb, I was told that there was only 982Gb left. The Vdisks are Vraid5. All the physical disks are in one disk group.

Our reasoning is that one disk per shelf is lost and also another two for the disk group, which would account for the 8Tb lost or used up in overhead or whatever.

Can someone confirm this is the likely case?

Kind regards
Darren Richards
Víctor Cespón
Honored Contributor

Re: Overhead on FATA 1GB Disks

VRAID 5 is created with 4 sets of data and one of parity. So 16 TB really take 20 TB of RAW space.

24 x 1 TB disks, with disk failure protection = single give you 20.4 TB of available space.

So with about 16 TB used you have almost all space used.
Rob Leadbeater
Honored Contributor

Re: Overhead on FATA 1GB Disks

Hi Darren,

Also remember that disks are sold with units based on the SI definition of tera (1000,000,000,000 bytes) whereas the EVA uses the binary definition. Taking that into account, your TB disks are only 931GiB in size - the formatted size might actually be slightly less.

That said, with single sparing you should still have raw space of (24 - 2) x 931 = 20482 GiB. VRAID-5 allows you to use 4/5 of that, so I'd have thought you should be able to get a useable total of 16385GiB.

I wouldn't run a disk group at that capacity however, especially with FATA disks...