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 Post subject: Expanding 8440 with more cages and relocate some disks
PostPosted: Wed Feb 19, 2020 2:50 am 

Joined: Mon Mar 04, 2019 8:57 am
Posts: 4
Hi all,
Need some advise about possible way how to go about this. I’ve inherited 2x 8440s that are equipped with 40x 3.89TB SSDs each. (Unfortunately, back then the administrator decided to go for such huge SSDs which are expensive, in any case I’m now stuck with these). The company has now decided to expand this storage but since the SSDs were too expensive the decision taken is to get 1.8TB SAS 10K disks.

Current Setup is :
4x node 8440
2x cages (4 in total including the controller nodes)
40x 3.84TB SSD (10 disks per shelf).

Attachment:
File comment: Existing Layout
existinglayout.png
existinglayout.png [ 98.92 KiB | Viewed 2765 times ]


The expansion will bring 6x shelves and 20 disks per site. The layout we were thinking of would be :
Attachment:
File comment: After Expansion
afterexpansion.png
afterexpansion.png [ 95.46 KiB | Viewed 2765 times ]


We understood that we can relocated the SSDs so that we achieve balancing across all enclosures but it seems that this is going to be a lengthy process. On the other hand we are thinking on migrating all data from one storage to the other, level one site and once finished migrated data back and do the other storage. We have enough capacity and this storage is still barely used.
What would be the correct procedure to balance the disks across all enclosures (the SSDs) keeping in mind that we don’t care of any data since this will be migrated. Should we just delete the current CPGs , remove disks and redistribute accordingly and re-create the CPGs again ? Is this be possible ? I’ve read somewhere that most probably we will need to re-initialize the whole storage again (contact HPE and re-initialize the storage to its mob).

Also what would be the recommended CPG config + step size if we would say that we are going to allocate 2 or 1 SSD per enclosure for AO while using the other SSDs for throughput hungry hosts and the rest of SAS disks for other applications?

Thank you
Etienne.


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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Wed Feb 19, 2020 6:01 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1021
Location: Europe
Are you planning on buying more drives? If not I would consider dropping the new cages and rather get 4 more 10k drives and install 6 in each cage.

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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Wed Feb 19, 2020 9:19 am 
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Joined: Fri Jun 21, 2013 1:03 pm
Posts: 109
Location: USA
Depends on availability needs, I'm guessing someone was planning on Raid6 8+2 config with doing cage level availability.

If you don't need the cage level availability, then I'd skip the extra cages unless your spindle count will grow into anytime soon.


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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Thu Feb 20, 2020 6:00 am 

Joined: Mon Mar 04, 2019 8:57 am
Posts: 4
Patrick/MammaGutt, we are going to buy more disks soon. We've opted to purchase the shelves right away else on the next upgrade we would need to get shelves with x amount of disks right away which makes eventual upgrades expensive.

What do you suggest do to in order to move the SSD disks to the other shelves ? Is my assumption correct i.e delete the CPGs, move the SSDs and re-create these ? Or we would need to get the support to take our storage to mob again after moving these disks ? We want to avoid the hassle of evacuating the data knowing that the only data we have can be deleted.

Thank you


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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Thu Feb 20, 2020 3:52 pm 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1021
Location: Europe
mulae wrote:

What do you suggest do to in order to move the SSD disks to the other shelves ? Is my assumption correct i.e delete the CPGs, move the SSDs and re-create these ? Or we would need to get the support to take our storage to mob again after moving these disks ? We want to avoid the hassle of evacuating the data knowing that the only data we have can be deleted.

Thank you


Deleting CPG doesn't do it. You need to empty the drives, dismiss them and re-admit them.

If you can empty the entire array, that will take less time than rebuilding it.

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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Fri Feb 21, 2020 1:33 am 

Joined: Mon Mar 04, 2019 8:57 am
Posts: 4
MammaGutt wrote:
mulae wrote:

What do you suggest do to in order to move the SSD disks to the other shelves ? Is my assumption correct i.e delete the CPGs, move the SSDs and re-create these ? Or we would need to get the support to take our storage to mob again after moving these disks ? We want to avoid the hassle of evacuating the data knowing that the only data we have can be deleted.

Thank you


Deleting CPG doesn't do it. You need to empty the drives, dismiss them and re-admit them.

If you can empty the entire array, that will take less time than rebuilding it.


So if understand correctly the only way to make the process faster would be to re-initialize the array to its mob ?

Thank you
Etienne.


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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Fri Feb 21, 2020 5:52 am 

Joined: Tue Nov 18, 2014 5:13 am
Posts: 17
Hello,

I had exactly the same issue last summer: I added two shelves on my 8440s with some 3.84T SSDs, , and rebalance the SSDs in all the shelves .

and the actual solution is so insanely simple, I ddin't believe it :

- just remove one live SSD from its slot, then put it to its new location

and.. that'all !
( as long as it stays on the same Node loop )

There is nohing special to do before (no dismisspd or anything), as long as you just move it in less than 30s, (so remove the cache on the target slot beforehand, then that's plenty of time for a 50cm move)


before proceeding to the next move, just to be cautious check that all of its chunklets are available again ( the unavalalbe counter might rise after the move, then drop slowly);

I waitedaround 5 minutes each before proceeeding to the next drive ( spamming showpd -c PDID in the mean time)

so, during lunch time I moved all 20 of them.

(I learned this tip fron guys from Antemeta, I didn't invent it)


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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Fri Feb 21, 2020 8:16 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1021
Location: Europe
aDelaloy wrote:
Hello,

I had exactly the same issue last summer: I added two shelves on my 8440s with some 3.84T SSDs, , and rebalance the SSDs in all the shelves .

and the actual solution is so insanely simple, I ddin't believe it :

- just remove one live SSD from its slot, then put it to its new location

and.. that'all !
( as long as it stays on the same Node loop )

There is nohing special to do before (no dismisspd or anything), as long as you just move it in less than 30s, (so remove the cache on the target slot beforehand, then that's plenty of time for a 50cm move)


before proceeding to the next move, just to be cautious check that all of its chunklets are available again ( the unavalalbe counter might rise after the move, then drop slowly);

I waitedaround 5 minutes each before proceeeding to the next drive ( spamming showpd -c PDID in the mean time)

so, during lunch time I moved all 20 of them.

(I learned this tip fron guys from Antemeta, I didn't invent it)

This sounds almost to good to be true.

Did the existing PDID update itself with the new cage/slot position or did you get a new PDID (and got stuck with a ghost ID)?

Also, do you know if there was any 3PAR OS requirement for this?

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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Fri Feb 21, 2020 10:08 am 

Joined: Tue Nov 18, 2014 5:13 am
Posts: 17
MammaGutt wrote:
This sounds almost to good to be true.

Did the existing PDID update itself with the new cage/slot position or did you get a new PDID (and got stuck with a ghost ID)?

Also, do you know if there was any 3PAR OS requirement for this?


it was truly magical, the position updated itself, no ghosts whatsoever, nothing to clean up manually; maybe it works only with SSDs?
( when the first time the tech told me that, I thought he was joking...)
durning this operation, I had an ssh session open on the array but was just to check the chunklets were all up to date before going to the next SSD move...

my arrays were on 3.3.1 MU2 + all the recommended patches from infosight at the time, last July.


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 Post subject: Re: Expanding 8440 with more cages and relocate some disks
PostPosted: Tue Mar 10, 2020 6:29 am 

Joined: Mon Mar 09, 2020 8:34 am
Posts: 1
Can we clarify if the above is 100% true?

I have 2 more cages to add to 2-node 8200, and I would like to move some of the disks from the top two original enclosures down to the bottom two to make it 100% balanced over all four cages.

Our array is still empty and has not gone into production yet, my plan was to connect the two extra cages empty, move the existing disks down to where they need to be, then plug in the new disks and add them to the existing CPG's.

Does that sound reasonable?


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