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Bhaskar11
2 Bronze

How to check amount of data written on a preallocated device.

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Hi all,

Good day !!

I have a customer who recently increased SG from 6TB to 12 TB . It consists of 12 devices 1 TB each. as indicated these devices are 100% preallocated. is there a way in EMC VMAX3 to find out how much data is written inside these devices ?

We have a way till VMAX2 where we can check how much data is written inside a 100% pre allocated device.

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PedalHarder
3 Argentium

Re: How to check amount of data written on a preallocated device.

I haven't seen what the output looks like for preallocated devices in V3, but try:

symcfg list -sid xx -pools -thin -v -detail

Then look at the section "other thin devices with allocations in this pool" It has for each device "Total Tracks", "pool Allocated tracks" and "pool used tracks"

BTW, for VMAX 3, is there a particular reason you are pre-allocating? Certainly prior to V3, there was a little latency overhead for allocating tracks on first write to the newly allocated space, but much improved in V3, so this should not be a consideration now.

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Bhaskar11
2 Bronze

Re: How to check amount of data written on a preallocated device.

Unisphere.JPG.jpgSymcli.JPG.jpg

I tried for device 00082 but it is not reflecting what I am looking for, output shows how much space I have booked from  pool . If a device is 100% preallocated it will show whole space .

Answer to your question Jason is ::: This is a government site due to policy restriction of government they allocate storage with preallocation factor.

Below is the o/p of a device from VMAX 20K , in VMAX20K we can see amount of data written in preallocated device as highlighted but I am unable to see amount of data written in VMAX3 device. I saw some article which says this is a limitation of VMAX3 but I am not sure.

VMAX2.JPG.jpg

If there is a limitation also please anyone briefly explain why is this limitation so that I can explain it to customer.

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Bhaskar11
2 Bronze

Re: How to check amount of data written on a preallocated device.

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PedalHarder
3 Argentium

Re: How to check amount of data written on a preallocated device.

Agreed, it looks like the quoted KB article is still accurate.

In terms of why this is the case, I'll provide my view - which is not necessarily the view of the product management team.

Over time, we have put R&D into the VMAX product development. From thick to thin and enhancements beyond the initial thin provisioning. One of those enhancements was to remove the performance overheads associated with allocating space on a first write to a thin provisioned volume. This was done with VMAX3 and so the need to pre-allocate from a performance perspective went away. Since VMAX 3 is a different technology to previous generations, the reporting changed with the evolving technology. There is not the same need to report on written vs. allocated.

In your example you are still pre-allocating. It would be interesting to know what the business justification is for this on VMAX3. If you think there is a valid justification to pre-allocate, then I recommend you make this known to your local account team and get an enhancement request raised for the reporting you are interested in.