Bug 1788347 - reduce min_alloc_size to improve space usage for small objects
Summary: reduce min_alloc_size to improve space usage for small objects
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Ceph Storage
Classification: Red Hat Storage
Component: RADOS
Version: 4.0
Hardware: Unspecified
OS: Unspecified
high
high
Target Milestone: rc
: 4.1
Assignee: Neha Ojha
QA Contact: Manohar Murthy
Karen Norteman
URL:
Whiteboard:
Depends On:
Blocks: 1816167
TreeView+ depends on / blocked
 
Reported: 2020-01-07 01:46 UTC by Josh Durgin
Modified: 2021-04-23 08:29 UTC (History)
11 users (show)

Fixed In Version: ceph-14.2.8-3.el8, ceph-14.2.8-3.el7
Doc Type: Bug Fix
Doc Text:
.Small objects and files in RADOS no longer use more space than required The Ceph Object Gateway and the Ceph file system (CephFS) stores small objects and files as individual objects in RADOS. Previously, objects smaller than BlueStore's default minimum allocation size (`min_alloc_size`) of 16 KB used more space than required. This happened because the earlier default value of BlueStore's `min_alloc_size` was 16 KB for solid state devices (SSDs). Currently, the default value of `min_alloc_size` for SSDs is 4 KB. This enables better use of space with no impact on performance.
Clone Of:
Environment:
Last Closed: 2020-05-19 17:31:40 UTC
Embargoed:
hyelloji: needinfo-

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Github ceph ceph pull 32998 0 None closed nautilus: common/options: bluestore 4k min_alloc_size for SSD 2021-02-15 15:18:57 UTC
Red Hat Product Errata RHSA-2020:2231 0 None None None 2020-05-19 17:32:13 UTC

Description Josh Durgin 2020-01-07 01:46:59 UTC 
Description of problem:
RGW or CephFS store small objects and files as individual objects in rados. Objects smaller than bluestore's min_alloc_size (16k for ssd) use much more space than required.

min_alloc_size of 4k has been shown to have no detriment to performance for SSD.
Use this as the default for SSDs.

How reproducible:
100%

Steps to Reproduce:
1. Write many 4k files to cephfs.
2. Run 'ceph osd df'

Actual results:
Raw space used is >16kib per object.

Expected results:
Raw space used is closer to 4kib per object.
Comment 2 Josh Durgin 2020-03-23 20:42:12 UTC 
included in 14.2.8 rebase
Comment 13 errata-xmlrpc 2020-05-19 17:31:40 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2020:2231
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