3 Silver

VMAX Virtual Provisioning and FAST VP

Hi ,

I have a question about Host LUN(Thin Devices ) on VMAX.

We have a set of RAID10 and RAID6 disks on which we have TDAT( Data Devices). Apporx size of each TDAT 64GB.

Now, I take it I will have to combine these Data Devices into a Pool (specific for each type of protection) .

Now on these pools , I will have to carve up Thin Devices. My question is what is the size of Thin Devices I have to choose ???

Can I choose any random cylinder count specific to user requirement or it has to be same as of TDAT's ??

Can I just make it all with specific fixed size ???

How can I best decide for the size of thin devices ? I take a thin device will be striped to all cylinders with the pool its bound too.

We do later intend to use FAST VP on volumes.

We do have a different LUN requrements for hosts from 50GB, 10GB 1GB to 1TB.

Thanks in advance.

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8 Replies
4 Beryllium

Re: VMAX Virtual Provisioning and FAST VP

Those TDAT sizes seem small, you want 8 physical hypers per drive or the minimum hypers to use all the disk.  For example, with 6+2 and 300GB drives, you would want your TDATs to be about 240GB each.

As for TDEV sizes, it really doesn't matter what the TDAT size is, just make your TDEVs to match your host requirements.  For host devices larger than 240GB you will need meta volumes.  Also consider striped meta volumes for those host volumes requiring high performance.

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3 Silver

Re: VMAX Virtual Provisioning and FAST VP

Hi Quincy,

Thanks for quick reply. For TDAT size we have 240GB on 2TB SATA , 6RAID6 (this will be 8 physical hypers) and 60GB(2 physical hypers) on RAID1 FC 600GB.

I take it TDAT are just like symdevs in DMX , addressable units, grouped into Storage Pools. Of course here in VMAX they will be used only in storage pools.

TDEV are addressable thin devs carved from Storage Pools and presented to Hosts.

Is my understanding above is correct ?

Why is it advisable to use larger TDAT’s ??

For TDEV’s choosing any size that matches host lun requirements will increase the overhead to mange it for every other hosts and also with Clones and SRDF devices needs size matching to source.

Can we choose any other better option or just like DMX agree on a fixed set of sizes ?

Regards,

Kavan

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4 Beryllium

Re: VMAX Virtual Provisioning and FAST VP

Too many backend devices will lower overall performance.  Too few will also limit performance.  We found the sweet spot to be between 8 and 16 hypers per physical disk.  With the 600GB drives and RAID1, you would want TDATs about 75GB to get 8 hypers per drive.

Again the size of the TDEV has nothing to do with the size of the TDATs, except for the total space they need in the pool.

If standardizing on a TDEV size makes administration easier, then go ahead and do that.

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3 Silver

Re: VMAX Virtual Provisioning and FAST VP

Gr8 , thanks a lot Quincy.

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7 Thorium

Re: VMAX Virtual Provisioning and FAST VP

Quincy56 wrote:

Those TDAT sizes seem small, you want 8 physical hypers per drive or the minimum hypers to use all the disk.  For example, with 6+2 and 300GB drives, you would want your TDATs to be about 240GB each.


Quincy,

can you show the math how you came up with 240GB TDAT size.

Thanks

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4 Beryllium

Re: VMAX Virtual Provisioning and FAST VP

A 6+2 volume is spread over 8 disks.  The data portion uses 6 of the 8 from a capacity point of view.  So a 240GB LUN takes up  40GB of space on each disk.  So with 300GB drives to get 8 physical hypers per disk, you want to create 37.5GB hypers or 225GB TDATs.

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7 Thorium

Re: VMAX Virtual Provisioning and FAST VP

thank you, i am trying to understand why you are using 240GB TDAT as your starting point ?

Is this correct calculation for 600G 3+1R5 ?

600 / 8 = 75G per hyper

75 * 3 = 225G optimal TDAT size ?

Thanks

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4 Beryllium

Re: VMAX Virtual Provisioning and FAST VP

The idea is to have at least 8 physical hypers per disk drive, or the minimum to use all the disk.

So for 600GB 3+1

600 / 8 = 75GB hyper on the disk * 3 for three data drives = 225GB TDATs.

In many cases it is impossible to have just 8 hypers, such as 14+1 on 2TB drives. The minimum splits on the disk in that case is 60.

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