Preallocated LUN (VMAX)

Thanks Saurabh. Any updated document shows this?

None that I am aware of?

the writes will go to the preallocated space first and then to unallocated. I am not sure if any primus article exist which states the same?

Hi Quincy - Can you pl guide me with one sample CLI command? eg - device 0F10

As far as I know, preallocated space is assigned to specific LBA ranges on the TDEV.  I would assume that a 50% allocated TDEV would have the first 50% of the LBA range to be allocated.  Any write past that point would be a new allocation.   Writes to the LBA addresses below the 50% would not create a new allocation.

This could easily be confirmed using a simple dd command with a count option.

It is the file system that is in control of where within the lun that new allocations are made. There is no CLI functionality that maps out LBA ranges by preallocated / written etc. Even if there were, how are you going to influence your file system to make the allocations in certain locations?

For example with a 1GB device, writing to 1/2 of it.

dd if=/dev/zero of=/dev/rdsk/c1t10d0s0 bs=512k count=1024

Hi Quincy - Thanks.

Is this command run at host level and can be run on production LUNs (I mean no performance impact while verifying the write counts) ??

Thanks in advance.

The command listed will write zeros to every block from the first block until the count specified.  So please don't run it against any device that has data you want on it.

I would suggest you create a new lun to run that command on and do not place any production data on it prior.