topic Re: Formula to calculate vraid5 estimate (or evaperf command) in HPE EVA Storage

Formula to calculate vraid5 estimate (or evaperf command)

Romain1 — Mon, 15 Mar 2021 14:20:27 GMT

Hello all,

I collect information about DiskGroup with the "evaperf dginfo" command.
This command gives me the total and used capacity of the diskgroup.

I would like also obtain vraid5 estimation.
After research, it seems that there is no evaperf command.

However, I read that there was a formula to calculate the vraid5 but I can't find a link to download the Excel file.

Do you have a formula to communicate to me with to calculate the vraid5 estimate (or possibly a command evaperf that I did not find) ?

PS : EVA4400 HSV300 model

Thanks & regards !

Re: Formula to calculate vraid5 estimate (or evaperf command)

Cali — Tue, 16 Mar 2021 12:39:45 GMT

Hi,

here is the formula:

Cali

Re: Formula to calculate vraid5 estimate (or evaperf command)

Romain1 — Wed, 17 Mar 2021 13:24:41 GMT

Hello Cali,

Thank you very much for your reply.
Unfortunately, I can't find the same result as the one indicated in the web interface. I have doubts about the data and the formula I use.
Example :

Below, the data I use:
m=4 (because RAID5)
p= ??? (I tried several values but how to find this value ? what is it ?)
N=36 (number of disks)
Xd=170 (because 15K drives)

Formula : X=1/(1-((3/4)*p)))*(36/4)*170

Can you help me? Or is there an EVAPERF command to get the estimated Vraid5 value available ?

Thanks & regards.

Re: Formula to calculate vraid5 estimate (or evaperf command)

Cali — Wed, 17 Mar 2021 14:37:07 GMT

Sorry, I misunderstood, you are looking for the Disk Space, this is different.

This Formula is for calculate the Safe IOPS, it's about performance.

evaperf is primary to show the Life Performance Data, so I expect you need performance Data.

There was a Tool that calculates the Space (NSS Sizer) but it is too old and no longer works.

You have Failure Protection = Single, this means 2 Disk for Spare.

The System calculates RSS Sets of Disks between 6 and 12.

So it should be 3x 8 Disk + 1x 10 Disk = 4x Raid 5 Parity Disk

In the end, you will have 36 Disk - (2x Spare Disk and 4x Parity Disk) = 30 Disk usable using Raid 5.

The target size of each redundancy set is eight disks, with a minimum of six and a maximum of 11. As disks are added to a disk group, the RSS automatically expands until it reaches 12 disks. At that point, it splits into two sets of six disks each. As more disks are added, one set increases from six to eight (the target size); then the remaining set increases. After all disks have been added to a disk group, each RSS contains eight disks, with the possible exception of the last set, which contains between six and 11 disks. This is why it is a best practice to add disks in groups of eight.

Cali

Re: Formula to calculate vraid5 estimate (or evaperf command)

Romain1 — Thu, 18 Mar 2021 07:48:31 GMT

Hello Cali,

Ok, no problem ! Maybe I didn't explain it well.
I would like to calculate the available Vraid estimate.

About NSS Sizer, with my resaerch, yes I heard about it.
I also heard about of "EVA Calculator" (HP_EVA_Calculator_v3.xlsx) but I didn't find it :(.

With the Summary information (screenshot above) :
Total disks : 36
Total capacity (raw) : 14521GB
Allocated (raw): 13041GB
Allocation level : 90%

Would it be possible to calculate the available Vraid estimate (even aproximately as indicated in the web interface) ?
I tried several options but have not yet found a solution.

Thanks and regards

Re: Formula to calculate vraid5 estimate (or evaperf command)

Cali — Thu, 18 Mar 2021 08:43:50 GMT

Sorry, that Formula not 100% correct.

The Spare is distributed over all Disks.

36 Disk > 3x 8 = 24, remain 12 > 4 RSS Sets with 1 Parity each

36 - capacity of 4 Parity Disks - capacity of 2 Spare = 30 Disk Netto with R5

Re: Formula to calculate vraid5 estimate (or evaperf command)

Romain1 — Thu, 18 Mar 2021 12:38:55 GMT

Cali,

Thank you for your reply.

Unfortunately, I can't find the same result as the one indicated in the web interface (vraid5 available : 483GB (see screeshot above)).

Excuse me for insisting but how do you calculate the available Vraid5 estimate with 30 disk (even aproximately) ?

Thanks and regards,

Re: Formula to calculate vraid5 estimate (or evaperf command)

Cali — Thu, 18 Mar 2021 13:15:32 GMT

It depends on the OS Version, and it's only an estimate.

First, the Storage is already 90% full and so I would not create any new Volume.

You have 625GB space free until raising the critical 95% and with Raid 5 (Parity overhead) this is about 435GB until raising the critical full.

I did not see any big discussion about +/-100GB, this is nothing and worst to think about.

Also, think about PDM, I add 2 Pictures here.

Disk group capacity (in GB) is presented differently for different versions of HP XCS controller software.

XCS 6.xxx, and XCS 09xxxxxx
• Maximum Vdisk Size, Vraid5. Shows the largest virtual disk that could be created in the disk
group, using Vraid5.

HP XCS 095xxxxx or later
The estimated capacity is based on factors, such as the estimated number and size of virtual disks
that you might typically create. The actual total capacity can be more or less than the estimates.
• Available, Vraid5. Shows the estimated capacity, if the entire disk group was used for Vraid5
virtual disks.

XCS 10000000 or later
• Available capacity (estimated). Shows the capacity remaining in a disk group if all new virtual
disks were to be created as either Vraid0, Vraid1, Vraid5, or Vraid6.
◦ Physical. This value is estimated from various factors such as the number and size of
virtual disks that might typically be created. The actual available physical capacity can
be more or less than the estimate.

Cali

Re: Formula to calculate vraid5 estimate (or evaperf command)

Romain1 — Fri, 19 Mar 2021 09:05:27 GMT

Hello Cali,

Yes, I know that the storage is already 90% full. This screenshot above it's just an example. I have several DiskGroup and bay EVA.

I would like to know how to find out the estimated Vraid5 value available without use web interface (with evaperf, formula,...). Just an estimate to have it in a monitoring tool .
Unfortunately, I don't know how to do it.

Thansk & regards,