HPE Storage Users Group

Hi all,

does anybody know a way to calculate or determine per cli the total usable capacity of a 3PAR-array?

Usable: Capacity you can use for your data and/or snapshots, without admin, spare or RAID-Overhead.

Given requirement: Only one CPG per disk type, as different cpgs (with different set sizes, RAID-types, ...) on the same discs make it impossible to know in advance how much data you can store.

showsys displays the total and allocated Raw-Capacity.
showspace -cpg <cpg> shows the remaining usable capacity.

But I don't have any idea how to display the total usable capacity of an array...

I got the numbers for one of our arrays from HP presales, but even with the correct answer, I can't find a way to get there by my own....

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When all else fails, read the instructions.

check out the following command:
showsys -space

It breaks down the capacity consumed. Let me know if you need more detail on any specific field/category.

Hi,

thank you for the tip, but as I wrote,



I would be happy to see the total usable capacity of an array. Not the still-free capactiy (showspace -cpg <whatever> does that job), but the overall usable capacity. Without RAID-OVerhead, spare, admin, ...

Management-Reporting, you know...

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When all else fails, read the instructions.

I think using showspace -cpg it should be LD Free +Usr Total = Total user space

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We don't have CPGs with different RAID characteristics on the samt disks or AO on our machines, so in theory it should be possible to calculate a "max LD space" on a systems that already has some data on it (and therefore, showspace -cpg only displays the remaining free space, and not the total usable space).

Funny enough, there is a way to calculate that number - from screenshots of the HP sizing Software. We were just wonderig how to get that number with build-in means...

For reporting, it feels more clean to get it from the machine and not to hard-code it in any scripts. As soon as you upgrade an array with new drives, you have to remember all places where you have to substitute old with new numbers...

_________________
When all else fails, read the instructions.

The sizing tool we use just calculates as if the entire tier/drive type was consumed by that one cpg ... just like showspace -cpg

The usable number is the EstFree ... LDFree is what can be actually consumed by a host and RawFree contains the Raid overhead on that

That output can be misleading if you choose an unbalanced CPG config to forecast ... a simple example would be a 4+2 Raid 6 on 8 drives. You will 2 drives worth of capacity that is "unreachable". On the other side, running a Raid 1 and Raid 6 on those same 8 drives will allow the system to consume 100% ... but forecasting on a split is difficult as you have to know how much will be consumed by each CPG.

Are you doing chargebacks or just forecasting array consumption?

I'm not 100% sure I understand what you're asking for, but since you'll never fill the box 100%, does a few GB's difference in you calcs make that much difference?

You can look at the free raw and space for a given class of disk "showsys -space -devtype FC" and look at the free initialized space, apply your overhead e.g 25% for 3+1 and then divide by 1024 and you have usable GiB's. You could do the same for total capacity rather than just free.

showsys -space -devtype FC
Free (15138816 * 0.75) = 11354112 / 1024 = 11088 GiB
Total (23396352 *0.75) = 17547264 / 1024 = 17136 GiB

Alternatively you could use "showspace cpgname" to forecast amount of free space available to a given CPG's or "showspace -t r5" to play what if, similar results but a bit more exact as it takes into account your CPG layout.

showspace -t r5 -ha cage -p -devtype FC
HA Cage (15118336 * 0.75) = 11338752 / 1024 = 11073 GiB

showspace -t r5 -ha mag -p -devtype FC
HA Mag (15130624 * 0.75) = 11347968 / 1024 = 11082 GiB

You could also work this backward based on the current CPG utilization. Failing that I'd look at writing a perl script or similar to pull the various numbers and provide the output you need.

I noticed to mentioned Admin space, unfortunately this isn't a fixed size and will depend on how you are using the system. But think of it this way, if you don't set aside admin space for metadata you don't get all the other 3PAR benefits.

Just my opinion but on a traditional array you know exactly to the GB how much space you have at any point in time because you've pre-configured and pre-comitted the space upfront. Get it wrong and you've wasted lots of space typically requiring a data migration or more usually additional disk to put it right. Then again who writes to 100% so knowing the exact to the GB is not really that useful from a practical point of view.

With 3PAR you don't commit things upfront and you can just change things on the fly, metadata gets you flexibility, so don't think about it as wasted or unusable space.

http://h20195.www2.hp.com/v2/GetPDF.asp ... 987ENW.pdf