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Feature #2003

limit XFS extent fragmentation for rbd

Added by Mark Nelson about 12 years ago. Updated almost 12 years ago.

Status:
Rejected
Priority:
Normal
Assignee:
-
Category:
librbd
Target version:
-
% Done:

0%

Source:
Tags:
Backport:
Reviewed:
Affected Versions:
Pull request ID:

Description

A user with the handle pmjdebruijn was asking earlier today about XFS extent fragmentation due to ceph writes on the freenode xfs channel. We should look into this for testing at some point.

We can use xfs_bmap to examine the extent ranges. Sample output from the user is here:

http://pastebin.com/xABVh19J

Suggestions from Christoph Hellwig are to use 512 byte inodes and set rbd_writeback_window to a large value. Sounds like typically there should be no more than 2-3 extent ranges for files of that size and the user is seeing 8.


Related issues

Related to Ceph - Feature #2052: librbd: caching Resolved

History

#1 Updated by Sage Weil about 12 years ago

Hmm, I'm don't think that rbd_writeback_window will help much here; it doesn't affect the size of IOs sent to rados.

Try setting 'filestore flusher = false' in ceph.conf for the [osd] section and see if that helps. You'll probably see latency go up periodically, but if the fragmentation improves we at least know what's going on.

#2 Updated by Sage Weil about 12 years ago

  • Tracker changed from Bug to Feature
  • Subject changed from XFS extent fragmentation due to ceph writes to limit XFS extent fragmentation for rbd
  • Category changed from OSD to librbd
  • Assignee deleted (Mark Nelson)

librbd caching will help a lot!

#3 Updated by Sage Weil almost 12 years ago

  • Status changed from New to Rejected
  • translation missing: en.field_position set to 1
  • translation missing: en.field_position changed from 1 to 1273

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