rwise1
1 Copper

Striped Meta Expansion / Clones / BCVs ?

I have to do various striped meta expansions. This works well but is a slow process, taking over 45 minutes to add 2 meta members to a 1.4 TB LUN for example, and is also somewhat restrictive, in that we can only expand by identical meta members, so for my 8-way 1.4 TB meta, with each meta member of 175 GB, I can only extend by increments of 175 GB. We have migrated onto EMC from HDS USP-V where expansions are much more flexible (even though USP-V is a much older environment than VMAX it can expand by any amount very fluidly) so the OS teams are critical of this limitation of VMAX.

I guess another option would be to clone the LUN to a larger target and then unmount the old LUN and present the copied one. However, this would require a Clone license, but we don't have that, so ... what other way is there to do this? Is it possible to create a larger LUN, then copy the data from a smaller LUN in there, and then present that LUN to the host?

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17 Replies
M_Salem
3 Argentium

Re: Striped Meta Expansion / Clones / BCVs ?

Hi rwise,

Welcome to EMC Community.

I tottaly understand the situation you are in. Expansion of devices on the fly is not supported with the current generations of VMAX (It is supported with other arrays like EMC VNX & CX). This feature will be addressed and supported in next generation of VMAX (VMAX V3).  Regarding your question about the clones, You can clone from a smaller device to a larger device however, you cannot restore data from the target device and bear in mind that you will be limited also to max device size on VMAX40K which is 240 GB so if you are going beyond this, then META devices should be considered.

Another restrictions we have for cloning metas is that source and target devices should have same configurations which means that:

Concatenated meta can only be cloned to concatenated meta and Striped meta can only be clone to striped meta with the same size/number of meta members and also same stripe size.

The only possible solution I can see for your case, is to leverge host based tools like PPME  (license is for free if you have a PP license) or OM (however this is for migration not cloning).

Hope this helps.

Mohammed Salem

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Dream93
2 Iron

Re: Striped Meta Expansion / Clones / BCVs ?

I may misunderstand your question. Here are few thoughts:

>>> it can expand by any amount very fluidly

It can be done in VMAX as well with concatenate as meta configuration. However as you said its not true for stripe meta - as data needs to be redistributed when adding a new stripe (when data integrity/preservation is requested)

>>> Is it possible to create a larger LUN, then copy the data from a smaller LUN in there, and then present that LUN to the host?


While expanding stripe meta, if one selects preserve data option then the data should be preserved (using BCV). Personally, Symm already does this efficiently, i don't think you will save any time by doing it manually. i may be wrong - but that's my expectation.


Btw, what is the main concern? is it regarding the time which symm is taking while expanding stripe meta (with preserving data)? Have you considered automating these using scripts - you can automate these steps either by SymmCLI cmds or ESI PowerShell Toolkit Cmdlets.


Hope this helps!


Regards.



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rwise1
1 Copper

Re: Striped Meta Expansion / Clones / BCVs ?

Time is not a concern. The main/only concern is internal departmental chargeback. i.e. if they want to pay for a 100 GB expansion, but I can only give them a 150 GB expansion due to meta member size limitations then that creates a billing nightmare. In large corporations with Enterprise storage arrays, chargeback like this is always a very important factor.

So, I would like to take a 1 TB striped meta and expand it to any size. What are my options?

- For striped meta expansion, I don't think I can do it any other way than preserving data, the only way I do this is via protecting the data on a BCV (but this limits me to incremental increases only of the meta member size, which leads to the "corporate chargeback nightmare" described above).

- Non-meta devices are not something that are important here. 98+ % of LUNs on our environment are striped metas (EMC wrote a guide in which they recommended 4-way metas for devices larger than 8 GB, 8-way for larger than 128 GB, 16-way for larger than 1920 GB, and 32-way for larger than 3840 GB). This is surprising to me, but note that this was not written by the customer - EMC wrote this recommendation for the customer, so we have to follow it - so almost everything is a striped meta).

- For clones, we do not have clone licenses, so that is impossible ...

When comparing 5 year old USP-V expansion to a brand new VMAX 40K, it is disappointing that the USP-V can do this far more flexibly than EMC's flagship enterprise product (and without any special licenses), so I want options whereby I can say "yes, the VMAX can do more and better than an ancient HDS product". So far, I have no option to do that. Surely there must be something on VMAX 40K that will allow me to do what a 5-year old HDS product can do without spending a huge amount on Clone licenses?

Is there is no way that I can create a 1.5 TB 8-way meta, and then migrate data from my existing 1 TB 8-way meta onto that meta (without Clone licenses)?

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M_Salem
3 Argentium

Re: Striped Meta Expansion / Clones / BCVs ?

Hello rwise,

For your last question, Host based migration tools can help however this will use some CPU cycles from your host.

For the question regarding chargeback, There is a multitenancy support for VMAX40 with Ionix StorageScope for chargeback however, I am not sure how can we utilize this in your existing system. and I doubt this will help to override the limitation we have for striped METAs expansion.

I will ask one of my colleagues to reply to you for a better answer.

Hope this helps.

Mohammed Salem

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rwise1
1 Copper

Re: Striped Meta Expansion / Clones / BCVs ?

Hi Mohammed, That would be fantastic if you or one of your colleagues could explain how to do this (i.e. simply expand a striped meta to any size arbitrarily). It shouldn't be too difficult to create a larger device/meta and copy the data from a smaller device/meta I hope, but if the only way is via a Clone license, then that would be disappointing (particularly when 5+ year old USP-V technology can do that seamlessly with ease and base functionality). I don't mind if it's complicated, I can script up anything if there is a process to get this to work. Many thanks.

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dynamox
6 Thallium

Re: Striped Meta Expansion / Clones / BCVs ?

i am afraid you will be disappointed, you can't expand a striped meta to any size you like.

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rwise1
1 Copper

Re: Striped Meta Expansion / Clones / BCVs ?

I know I can't do that, but what about other options? Is there no posibility to create a different larger sized BCV meta and copy data in there and then convert that to a TDEV meta and present to a host for example, or some other option?

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dynamox
6 Thallium

Re: Striped Meta Expansion / Clones / BCVs ?

can't do that either, only options are M.Salem already mentioned, host based migration: either using PowerPath Migration Enabler or native LVM/ASM tools. Now if you are willing to take downtime there is always robocopy/rsync. Create a custom size device, present it to the operating system, shutdown application and copy the data.

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rwise1
1 Copper

Re: Striped Meta Expansion / Clones / BCVs ?

Downtime is mostly ok for this client. Robocopy is great, but in my experience when we have filesystems with 100's of thousands of files, it can be very slow. but never got around to using PPME so that would be good (but unfortunately they use native multipathing on Windows 2008 / Solaris / Linux here so no PowerPath except on Windows 2003). I'd like to try out Open Migrator (but as file-based it will probabaly have the same limitation as robocopy). Are Open Migrator licenses free?

I've done 2 or 3 thousand host migrations on Open Replicator (my favourite migration tool), but I've only ever done that array to array. Long-shot here, but is it possible to OR internally between LUNs in the same array? That could work quite well (if it was possible).

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