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October 15th, 2015 13:00
Tdev migration
Hello everyone,
I have a vmax 20k which uses thin provisioning and allocates tdevs to a vplex. vplex then carves out storage from this tdev and presents to the hosts. There is a need to move the data to another storage array (not necessarily a vmax) using recoverpoint or host based migrations. What type of array based and host based migrations can preserve the thin lun after it is migrated to new array?. I dont want the lun to lose all its unallocated space after the migration so i need to know which methods will preserve the thin feature of the LUN and which ones will not. Please assist. Thank you.
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echolaughmk
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522 Posts
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October 19th, 2015 04:00
Hi,
LVM host-based migrations for the most part will likely not be thin-aware if you have logical volumes that consume the entire disk, but maybe the FS is not 100% full.
Having VPLEX at the target changes the answers a little bit because the VPLEX does not support the UNMAP SCSI command. This means that if the migration involves you issuing manual reclaims at the host level after the migration is completed, the VPLEX will not pass those commands to the array to reclaim. This means that you might want to migrate to the native array to get the space savings and then encapsulate as a thin device under VPLEX.
There are a variety of tools that aren't thin aware from a migration perspective (probably too many to list and that I have used given the different array tools out there..haha). What I would do it determine what operating systems you have to migrate, what the source and end migration targets are (sounds like VPLEX in this case) and then you can narrow it down to what is supported. If these VPLEX clusters are in a Metro, you could just create a DR1 device and drop the source leg as another migration alternative as well.
echolaughmk
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October 16th, 2015 04:00
What is your target array? Is it an EMC array or non-EMC?
Here are some options assuming EMC and non-EMC arrays
- RecoverPoint will be thin aware if you create another copy of the LUN to cut over to
- PPME (PowerPath) host copy should also be thin-friendly with regards to doing a host-based migration
- As for LVM...that will depend on the OS - some do and some don't. Volume Managers like VxVM have technology like SmartMove for this at the LV level. Other LVMs might not be as friendly.
- If you put the target array behind vplex and it is built on thin volumes, VPLEX should be thin-aware as well if you check the "thin rebuild" option and create a mirror through VPLEX on it...or possibly do a data mobility job (I forget if this is thin aware off the top of my head...I think it is).
- If Open Replicator is a possibility, that has front-end zero detection in some of its migration scenarios
Regardless of the migration technology and testing which one works best, if the target array supports unmap you should be able to migrate it worse case and inflate the device and then execute host tools to run an unmap on the target array - tools like EXT4 in linux, vmkfstools in VMware, sdelete in Windows, thin reclaim in Veritas, etc. I know its not pretty but it could be used if none of the options above give you the result you are looking for with not copying zeros.
I realize it is not a concrete answer given it depends on other environmental not know...but hopefully this starts the thought process.
NAS_Person_2010
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October 16th, 2015 08:00
Thank you echolaughmk for your answer. Very helpful. So, I guess, most of the migration technologies are thin aware and will maintain the same allocated space in the thin LUN during and after the migration. Let me ask this question in a different way then : Which migration technologies (host based/array based) are NOT thin aware. Also, are there things to watchout during host based migration of thin lun that may use up the all of the unallocated space during/after migration. This questions is specific to the scenario where there is a vplex with vmax at source location and vplex with possible non-emc array at target location Please let me know. Thank you