HPE Primera free space

[Aleksey_430]

Hi!

Need help understanding free space on my primera. 

There are eight SSD drives with a capacity of 3,575 GiB, raw capacity 28,600 GiB. Maximum CPG size when creating - 15102 GiB. Why so few? Okay, according to my calculations, RAID6 + 2p gives about 21500 GiB. 

In the System menu, Allocated Capacity bubble shows - System 8,445 GiB. What is included in the system area?  .mgmtdata+ .srdata+admin=602GiB. Maybe it includes parity chunkles? But it's one disc (3575GiB).

Inside the CPG, nothing is clear either ... I have 8 VV with thin provisioning. Total used space after data reduction, in the "Total used" field - 7558GiB.  And I see this figure in CPG properties - "Private base - 7558GiB" 15102-7558=7554GiB. So much free space I expected.

But also, there is a field "Shared - 4200GiB" - what is this value? And along with this value, Estimated free usable CPG capacity, only 3,378 GiB.

[sbhat09]

Hello @Aleksey_430,

Space calculation on Primera will be as below:

1. Drives capacity is not 100% usable. You can use only around 90% of drive capacity. So, your 3575gb drive can produce only around 3200 chunklets (of 1gb each).
2. Among them, around 7%-13% of the chunklets will be reserved as spare chunklets. This spare chunklet reserve depends on type of sparing you selected while initializing the system. Minimal - around 7%, Balanced - around 9%, maximal - around 12%. Considering the maximal sparing, available chunklets per drive are 2800.
3. Then the system applies RAID-6 (6d,2p) on those available chunklets. So, usable space reduces to around 2100gb per drive.
4. In the available space (2100*8=16800gb) some space will be occupied by mgmtdata, .srdata, admin volumes.

If you calculate the space after considering the above, numbers look closer to real values. Please let me know if you have any questions. 

Regards,
Srinivas Bhat

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[Aleksey_430]

Now it's a little clearer. When initializing the system, 1% -3% -1% was suggested. Looks like some kind of bug. Balanced was my choice. Considering this, 15GiB looks to be the right one..

There is one question left.
Can you tell me what "Private base" and "Shared" means on the CPG Capacity Summary page?

[sbhat09]

Hello @Aleksey_430,

What is the OS version of your Primera system? Can you please share the screenshots of 'Private base' and 'Shared' capacity?

Regards,
Srinivas Bhat

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[Aleksey_430]

Unable to load image.
HPE Primera version - 4.4

CPG image 

[sbhat09]

Hello @Aleksey_430,

1. Private base - The space occupied by the base volumes to write data (private space for the base volumes)
2. Private snap - The space occupied by the snapshots to write data (private space for the snapshots)
3. Shared - The space shared by volumes due to deduplication. This space belongs to some data shared by multiple data pointers. (If there is no deduplication, shared space will be 0)
4. Free - The unused space within the LDs. Every LD is constructed with 8 chunklets of 1 gb each (6 data, 2 parity) if the data chunklets are not fully utilized, they qualify to be in this category.

'Estimated free usable CPG capacity' is outside the above 4 classifications. The capacity shown here is the space available after applying the CPG specific RAID.

Regards,
Srinivas Bhat

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[Aleksey_430]

@sbhat09 

Thank you. I thought so.
But sad that the information about VV is not reliable.

Info   

The screenshot shows that the hosts recorded on CPG 17527GiB. After data reduction, the "Totsl used" field indicates 7370, which is roughly equal to the "Private base" field in the CPG window. BUT! "Shared" data is not in the VV information. It's confusing. And it does not give correct information about the occupied VV space.

[sbhat09]

Hello @Aleksey_430,

As per the screenshot 7395gb is the unique data (private base). Additionally, there is 4311gb of shared data by multiple pointers (due to deduplication). They are counted mutually exclusive.

Ex: There are unique blocks of 1 gb each A, B, C, D. and the block E is shared by 4 pointers (deduplicated data). Here the volumes claim that 8gb data has been written. But storage shows 5gb is written (4gb private base, 1gb shared). The mystery of 3gb is hidden in the deduplication.

Regards,
Srinivas Bhat

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[sbhat09 · Accepted solution]

Hello @Aleksey_430,

Hope you found that explanation useful. Please let me know if you need further assistance on this.

Regards,
Srinivas Bhat

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[Saeid_66]

Hello

Best practice To calculate the number of LUNs in a CPG in primera ?

Thank you

[sbhat09]

Hello @Saeid_66,

Just run the command 'showcpg' in CLI like this, it will list the number of VVs (LUNs) in each CPG.

                           ----- showcpg -----
                       ----Volumes---- -Usage- -------------(MiB)--------------
Id Name   Domain Warn% VVs TPVVs TDVVs Usr Snp     Base    Snp    Free    Total
 0 FC_r1  -          -   0     0     0   0   0        0      0       0        0
 1 FC_r5  -          -  20    20     0  20  20 10264704 153728 1705728 12124160
 2 FC_r6  -          -   1     0     0   1   1     6144    768   36096    43008
 3 SSD_r1 -          -   0     0     0   0   0        0      0       0        0
 4 SSD_r5 -          -  10    10     0  10  10  3613952  58624  126464  3799040
 5 SSD_r6 -          -   0     0     0   0   0        0      0       0        0
-------------------------------------------------------------------------------
 6 total                                31  31 13884800 213120 1868288 15966208

Regards,
Srinivas Bhat

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[Saeid_66]

Thanks, but I want to calculate how many LUNs I can create with Raid_6, relative to the total CPG space I have.

Thank you

[sbhat09]

There is no limit on how many LUNs (thin provisioned or TPVV) you can create in a CPG. But the overall used size of the LUNs may not exceed the available space.

Ex: Suppose you have 10TiB free space. And you created 2 CPGs. There is not limit for any CPG to use space. Also there is no limit for number and size of the volumes you create. Only limit is overall consumption may not exceen 10TiB.

Regards,
Srinivas Bhat

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[Saeid_66]

True, but because I want to create Thin provision, I want to know how to get the number of LUNs, for example, I have a 10TB CPG SSD and 5TB CPG FC, Considering that from Raid_6 and I want to use thin provision. How many LUNs can I create? What is the formula?

[sbhat09]

Hello @Saeid_66,

There is no limit for the number of LUNs you can create, there is no formula to arrive at a number on this.

If the available space of the CPG is 10TiB, you can create as many volumes (thin provisined) as you want. Because thin provisioned volumes don't reserve any defined space. Ex: If I create a 4TiB volume, it doesn't reserve 4TiB in the CPG when created. It will reserve the space only to the extent how much physical space is actually utilsed (considering data reduction technologies like deduplication and compression). So, if 10TiB is the available space, you can still create 50 volumes (LUNs) of 4TiB each. There will not be any issues as long as all 50 volumes together utilise 10TiB physical storage space.

It is like if your car has 50 liters of fuel and efficiency is 12km/liter, how many times you can travel. Actually there is no limit on how many times you can travel. If your travel distance is within 5kms, you can travel over 100 times. If your travel distance is 100kms, you can travel around 6 times. The limit is as many times or as long as you have fuel in the car.

Like that thin provisioned volumes don't have any limit on the number/size of the volumes against the available storage space. The limit is on the overall utilization of the actual physical space.

Regards,
Srinivas Bhat

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Note: All of my comments are my own and are not any official representation of HPE.