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 Post subject: 3par 7200 DDS Space Issue
PostPosted: Thu May 09, 2019 8:58 pm 

Joined: Thu May 09, 2019 8:29 pm
Posts: 9
Hi, I'm currently facing an issue where the DDS volume is consuming too much space despite showing very little deduplication saving ratios.

Below is an output of what I get when I run showvv -s. I've also enabled "setclienv showsysobjs 1" to show the dds. I've removed the column for the names of the volumes for privacy reasons. I also only have 1 CPG consisting entirely of SSDs.

How is it possible that the DDS is consuming 12TB worth of space when there is only a dedupe ratio of 1.1 overall?

I'm trying to convert all the TDVVs to TPVVs in order to release space from the DDS but there simply isn't enough space to do so. AFAIK, you need enough free space equivalent to that of a volume within your CPG in order to convert it from TDVV to TPVV.

My volumes are 5TB in size and I only have about 2.7TB in raw capacity available right now. Is there anything I can do to resolve this issue?

HPE 3PAR OS version: 3.2.2.709 (MU6)+P99,P115,P119,P126

----Adm---- ---------Snp---------- --------------Usr--------------
---(MB)---- --(MB)--- -(% VSize)-- ------(MB)------- --(% VSize)-- ------(MB)------- -Capacity Efficiency-
Id Prov Type Rsvd Used Rsvd Used Used Wrn Lim Rsvd Used Used Wrn Lim Tot_Rsvd VSize Compaction Dedup
1 full base 0 0 0 0 0.0 -- -- 61440 61440 100.0 -- -- 61440 61440 -- --
37 dds base 35712 35087 0 0 0.0 -- -- 15084160 12082465 18.0 -- -- 15119872 67108864 -- --
0 full base 0 0 0 0 0.0 -- -- 10240 10240 100.0 -- -- 10240 10240 -- --
45 tdvv base 256 2 0 0 0.0 -- -- 1025 3 0.3 0 0 1281 1024 193.9 3.3
42 tdvv base 1648 1390 0 0 0.0 -- -- 599563 470052 89.7 0 0 601211 524288 1.1 1.1
44 tdvv base 1595 1315 0 0 0.0 -- -- 574278 451742 86.2 0 0 575873 524288 1.2 1.0
47 tdvv base 12672 12262 0 0 0.0 -- -- 4910593 3878699 74.0 0 0 4923264 5242880 1.3 1.2
41 tdvv base 15057 14652 0 0 0.0 -- -- 5965586 4680280 81.2 0 0 5980643 5767168 1.2 1.1
46 tdvv base 14468 14098 0 0 0.0 -- -- 5539867 4304523 82.1 0 0 5554335 5242880 1.2 1.0
-----------------------------------------------------------------------------------------------------------------------------------------
9 total 81408 78806 0 0 32746752 25939444 32828159 84483072 1.3 1.1


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File comment: Attached screenshot of showvv -s.
Space Issue.JPG
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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Fri May 10, 2019 4:35 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 971
Location: Europe
If you compare Usr Used and Usr Rsvd on the DDS you can see that you have about 3TB of free space inside the DDS to grow.

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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Fri May 10, 2019 11:34 pm 

Joined: Thu May 09, 2019 8:29 pm
Posts: 9
Why is the DDS so big when the dedupe savings is so small? I'm actually only using around 15 TB of space but the DDS itself has reserved way too much space. I really wish I could just remove it and return to using TPVVs instead.

Is there a way to shrink the DDS? The problem with using it as if currently is is that if the raw capacity gets too low, the san itself will stop IO.


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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Sat May 11, 2019 12:17 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 971
Location: Europe
Why do you think DDS size and dedupe ratio is related?

Dedupe ratio depends on the uniqueness of the data, while DDS depends on size.

With 7k I don’t think the DDS will shrink (unless you remove all dedupe volumes). It does however defrag so deleted data is released within the DDS, but not reclaimed outside the DDS.

It will not stop IO until it is 100% full as long as the system is configured correctly (hardware balance).

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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Sat May 11, 2019 2:05 am 

Joined: Thu May 09, 2019 8:29 pm
Posts: 9
Right, I think I understand what you mean.

Given the size of my DDS.. would this mean that it is storing 12TB of unique data for reference? What if the next few TB of data that is written to my array happens to also be unique as well...

As it currently stands, I have 16TB worth of space allocated to volumes and 12TB automatically allocated to the DDS as a reference for data savings. The total capacity of my array is 28.5TB. If I allocate any more volumes and they happen to be unique blocks that are not referenced within the DDS then I'm screwed.


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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Sat May 11, 2019 2:09 pm 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 971
Location: Europe
The DDS has allocated 15TB and 12TB of that is used. The DDS in your configuration contains 1 copy of any block stored on dedupe volumes. So if you have one block which is stored on multiple volumes it is stored once in the dedupe and referenced to all volumes(basically this is how dedupe works :)). With TDVV1/2 (any CPG created before 3.3.1) both blocks that dedupe and not is stored in the DDS.

If you add 1TB to the array on a dedupe volume it will be stored in te DDS. If it doesn't dedupe at all, you will have used 13TB of 15TB allocated in DDS.

If your DDS fills to 100% and your array fill to 100% you are pretty close to screwed.

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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Sun May 12, 2019 8:38 pm 

Joined: Thu May 09, 2019 8:29 pm
Posts: 9
Thanks for the explanation, MammaGutt. Much appreciated.

Would you also happen to know if there are additional space requirements for converting a TDVV to TPVV via the convert volume function on SSMC? I remember reading somewhere that you may need enough space for the array to do a snapshot of the volume during the conversion process. I.e. To convert a 5tb volume, I would also need 5tb of free raw capacity readily available. Is this correct?


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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Sun May 12, 2019 11:47 pm 

Joined: Mon Sep 21, 2015 2:11 pm
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Location: Europe
I think you need at least enough free space as the VV you are converting. So 5TB VV would require ~6-7TB of RAW depending on RAID level/overhead.

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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Sun May 19, 2019 8:21 pm 

Joined: Thu May 09, 2019 8:29 pm
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Is there any way to reduce the reserved space of the DDS?


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 Post subject: Re: 3par 7200 DDS Space Issue
PostPosted: Mon May 20, 2019 4:55 am 

Joined: Mon Sep 21, 2015 2:11 pm
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With a lot of patience maybe.... From what I understand this was one of the major things changed with tdvv3 (tdvv cpgs created on 3.3.1)

With the old dedupe, the only quick way to recoup is to migrate the entire cpg to tpvv and release the entire dds in one go.

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