Describe the issue:

In the "Administration Guide, Chapter 9.6" Of RHCS4 document it is mentioned that In BlueStore, the raw partition is allocated and managed in chunks of bluestore_min_alloc_size. By default, bluestore_min_alloc_size is 64 KB for HDDs, and 16 KB for SSDs. 

But from RHCS 4.1 the default value of bluestore_min_alloc_size for solid state devices(SSDs) has been changed from 16KB to 4KB. The current value of bluestore_min_alloc_size_ssd is 4 KB.

The same has been included in the release note of RHCS 4.1 but not in the  "Administration Guide, Chapter 9.6" of RHCS4 document.

In RHCS 4.1 and Newer:
#ceph daemon osd.0 config show | grep bluestore_min_alloc_size_
    "bluestore_min_alloc_size_hdd": "65536",
    "bluestore_min_alloc_size_ssd": "4096",



Suggestions for improvement:
Requesting to make the change in the RHCS4 document about the statement of bluestore_min_alloc_size for solid state devices(SSDs) to 4KB in the "Administration Guide, Chapter 9.6" as well.

  Currently in the document:
  In BlueStore, the raw partition is allocated and managed in chunks of 
  bluestore_min_alloc_size. By default, bluestore_min_alloc_size is 64 KB for 
  HDDs, and 16 KB for SSDs.

  Expected change in the document:
  In BlueStore, the raw partition is allocated and managed in chunks of 
  bluestore_min_alloc_size. By default, bluestore_min_alloc_size is 64 KB for 
  HDDs, and 4 KB for SSDs.


Document URL:
https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/4/html/administration_guide/osd-bluestore#tuning-ceph-bluestore-for-small-writes_admin

Chapter/Section Number and Title:
9.6. Tuning Ceph BlueStore for small writes

Product Version:
Redhat Ceph Storage 4

Any other versions of this document that also needs this update:
The changes are implemented on RHCS 4.1. But we have a common "Administration Guide" for all RHCS4.So the change expecting in the Administration Guide.

Additional information:
We have a KCS for the same issue described:
https://access.redhat.com/solutions/3829321