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Bug 1693381

Summary: Update EC document for luminous EC changes
Product: [Red Hat Storage] Red Hat Ceph Storage Reporter: Vikhyat Umrao <vumrao>
Component: DocumentationAssignee: Aron Gunn <agunn>
Status: CLOSED CURRENTRELEASE QA Contact: ceph-qe-bugs <ceph-qe-bugs>
Severity: high Docs Contact:
Priority: high    
Version: 3.2CC: agunn, asriram, kdreyer, tchandra
Target Milestone: z2   
Target Release: 3.2   
Hardware: x86_64   
OS: Linux   
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Last Closed: 2019-08-26 06:55:25 UTC Type: Bug
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 1685931    

Description Vikhyat Umrao 2019-03-27 17:15:29 UTC 
Description of problem:
Update EC document for luminous EC changes

Here in EC guide - 
https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/3/html/storage_strategies_guide/erasure_code_pools

and in configuration guide 

https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/3/html-single/configuration_guide/#settings

this new option - "osd pool erasure code stripe unit" which replaced old option "osd pool erasure code stripe width" from RHCS 2. 

Version-Release number of selected component (if applicable):
RHCS 3
Comment 1 Vikhyat Umrao 2019-03-27 17:16:29 UTC 
Details are given in this commit.

https://github.com/ceph/ceph/commit/930eae214c54f5e0e790c09f35da14dff8585ac1
commit 930eae214c54f5e0e790c09f35da14dff8585ac1
Author: Josh Durgin <jdurgin>
Date:   Mon Feb 13 17:42:33 2017 -0800

    OSDMonitor: get stripe_width via stripe_unit in ec profile
    
    With bluestore, making the smallest write match min_alloc_size avoids
    write amplification. With EC pools this is the stripe unit, or
    stripe_width / num_data_chunks. Rather than requiring people to divide
    by k to get the smallest ec write, allow it to be specified directly
    via stripe_unit. Store it in the ec profile so changing a monitor
    config option isn't necessary to set it.
    
    This is particularly important for ec overwrites since they allow random i/o
    which should match bluestore's checksum granularity (aka min_alloc_size).
    
    Signed-off-by: Josh Durgin <jdurgin>