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 Post subject: space reclamation - the most effective way
PostPosted: Wed Apr 04, 2018 6:40 am 

Joined: Fri Nov 25, 2016 7:07 am
Posts: 4
Guys, help a noob with the best space reclamation please. We operate VMware 5.5 and 6.0 environments with several Win2008 and CentOS/linux legacy systems so TRIM functionality is a problem for us. 100% virtualized environment, thin provisioning on virtual machines. Some 3Par VVs are thin, majority is dedup. Model 20850, 32x 4TB SSD, OS 3.2.2MU6, single CPG (Raid5 due to space efficiency, we didn't need anything else ; performance is very fine - we are hardly getting below 30.000 IOPS all day long, quite usually above 150.000 IOPS and 3GB/s and almost always with sub-1ms latencies).

Over the time, we accumulated lot of ballast. What would potentially be the best way how to deal with the situation ?

- convert existing thin VVs to dedup
- compact CPG


- delete unnecessary data within virtual machines (yay, sounds easy).
- overwrite unused space within virtual machines with zeros. Several OS-dependent tools available to do this.
- reclaim unused space on VMware datastore level (esxcli storage vmfs unmap --reclaim-unit=200 --volume-label=XXXXX)
- let it sit overnight or two days, so 3Par ASIC can do its job and detect 0s
- compact CPG again




Overwriting unused space within virtual machines with 0s will effectively inflate their thin provisioned disks on VMware level, so we have to have enough space available on datastore levels. This way, thin allocation of disk space will be shifted from virtual machine/VMware level to 3Par storage level but we are fine with that.

What have I forgotten ? Any other tips how to maximize compression and dedup on 3Par ? Big thanks for your time and advice in advance !


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 Post subject: Re: space reclamation - the most effective way
PostPosted: Wed Apr 04, 2018 1:12 pm 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1570
Location: Europe
lubomirz wrote:
What have I forgotten ? Any other tips how to maximize compression and dedup on 3Par ? Big thanks for your time and advice in advance !


Things that come to my mind.

1. RAID 5 on large SSDs are dangerous. I don't think you find a single vendor in the industry recommending anything with less than double parity today. Remember that you don't need a dual disk failure to have an issue with RAID5 ... you just need a single disk failure and an unrecoverable read error on any of the other drives in that RAID set to be screwed. With increasingly larger SSDs this is a serious issue. Just google RAID5 and URE.
2. Without UNMAP in Vmware (require VMFS6 and ESXi 6.5 or later), the correct way is thin (both dedupe and compression are thin volumes) on 3PAR and Eager Zero Thick in Vmware. With UNMAP, the correct way is thin on thin.
3. Run unmap command from ESXi(esxcli storage vmfs unmap something somethinf if my menory serves me right). Disclaimer, the command is "fast", but it takes a long time to reclaim the space(could take weeks to reclaim everything). You can tune/convert from thin -> full -> thin to speed up the process. Not recommeded if doing dedupe.
4. There is a dedupe estimator available on the 3PAR. Test it after reclaiming prior to converting. There is a best practice document available ( https://h20195.www2.hpe.com/v2/GetPDF.a ... 524ENW.pdf ) which covers a lot of details about everything. Not sure if it's in that or another reference document but you should always test your dataset prior to converting to dedupe. If you get less than 1.3:1 or something it might not be worth doing.

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 Post subject: Re: space reclamation - the most effective way
PostPosted: Thu Apr 05, 2018 5:06 am 

Joined: Wed Nov 09, 2011 12:01 pm
Posts: 392
Also worth noting that if you are planning to update to 3.3.1 mu2+ when released then you'll need to have space to duplicate all your dedup volumes to move to the new dedup version. So you might want to do the other tasks first and pause before deduping more VVs till after the upgrade.

That doc above might also be the one mentioning block sizes and thin reclaim/dedup/compression efficacy gains, worth noting for future VMs.


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 Post subject: Re: space reclamation - the most effective way
PostPosted: Fri Apr 06, 2018 5:24 am 

Joined: Wed Dec 04, 2013 6:14 am
Posts: 15
lubomirz wrote:
What have I forgotten ? Any other tips how to maximize compression and dedup on 3Par ? Big thanks for your time and advice in advance !


We do practically the same thing, but we defrag the VM before running sdelete or similar to have as much continuous free space as possible.

Also the following can get you a few GB's back from each windows VM if you haven't runned it for a few windows update cycles: dism /online /cleanup-image /startcomponentcleanup /resetbase

And to maximize dedupe you should format your drives with a blocksize of something that divides on 16 (for example 16k, 32k or 64k), as the 3par dedupe use 16k pages. (windows default is 4k).
Though I'm not sure if this is still valid for InformOS 3.3.x on the new dedupe algorithm.


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 Post subject: Re: space reclamation - the most effective way
PostPosted: Sat Apr 07, 2018 3:22 pm 

Joined: Fri Jan 20, 2017 9:39 am
Posts: 58
mastrboy wrote:

We do practically the same thing, but we defrag the VM before running sdelete or similar to have as much continuous free space as possible.

Also the following can get you a few GB's back from each windows VM if you haven't runned it for a few windows update cycles: dism /online /cleanup-image /startcomponentcleanup /resetbase


I always like these discussions since I'm always on the lookout to make my Windows images better :)

If your 3par is all SSDs, is there any point to doing a defrag? Assuming the right conditions, if you're thin in vmware then windows won't defrag your disks anyway since it detects them as thin. If you're thick in vmware I think it will do the defrag but if you're backed by SSDs on a 3par, is there any point? I've stopped doing defrags a while ago since I don't think it helps much with a 3par with SSDs.

I do run sdelete to free up space since I don't have auto unmap at the moment and then holepunch the vmdk to make it that much faster to clone.

For the dism command, I've taken to running windows maintenance from the control panels twice after doing updates to do all the cleanup and reclaim space. I think it ends up doing something similar to your commend but that command is something i've been meaning to investigate.


mastrboy wrote:
And to maximize dedupe you should format your drives with a blocksize of something that divides on 16 (for example 16k, 32k or 64k), as the 3par dedupe use 16k pages. (windows default is 4k).
Though I'm not sure if this is still valid for InformOS 3.3.x on the new dedupe algorithm.


I'm no expert but I believe 16k is still the magic number. I've found nothing to say otherwise as of yet.


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 Post subject: Re: space reclamation - the most effective way
PostPosted: Sun Apr 08, 2018 7:37 am 

Joined: Tue May 05, 2015 10:56 am
Posts: 44
If your 3par is all SSDs, is there any point to doing a defrag?

Yes, its not about access times on the array, its about contiguous space in the VMDKs. If that is fragmented, the free space will not be freed on the array as the zero detect only works on 128MB blocks, so if you don't have 128MB free contiguous space in your VMDK it will not release it on the array. The exception to this is if you are using thin provisioned on the VMDK and have unmap working, as the VMDK will be shrunk.
The second thing this does it help with the OS on allocation, if you defrag the drive you will reduce the time taken for the OS to find and allocate space for large files.


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