Description of problem:
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LVM cache uses the mechanism to add fast device(SSD) to slow device (HDD) in the same Volume Group(VG), to make fast device(SSD) to act as a cache for slow device.

In this case, fast device(SSD)'s disk block size should be same as that of the disks in that VG. 

Also VDO volume is now created with disk block size as 4K. In this case, SSD that gets attached to thinpool created with VDO devices, should have its block size as 4K.

If the above compatibility is not present, RHHI-V deployment will fail

Version-Release number of selected component (if applicable):
-------------------------------------------------------------
RHHI-V deployment guides 1.8

How reproducible:
-----------------
Always

Expected results:
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Deployment guide of single node, 3 node, RHEL based guides, should add this to requirements for 'Disk'
1. If there is plan to make use of LVM cache for VDO devices, then the block size of that fast device(SSD) should be 4K
2. If LVM cache is used for non-VDO devices, make sure that the disk block size of slow device(HDD) and fast device(SSD) matches.