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(Contingency Plan)
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== Contingency Plan ==
== Contingency Plan ==
<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages). If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
* Contingency mechanism: (What to do?  Who will do it?) N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
* Contingency mechanism: Revert the shipped configuration of the relevant packages.
<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
* Contingency deadline: beta freeze
* Contingency deadline: N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
* Blocks release? No
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
* Blocks release? N/A (not a System Wide Change), Yes/No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
== Documentation ==
== Documentation ==

Revision as of 21:46, 8 July 2013



Using recent kernel (3.9 and later) features for (fast) SSD caching of (slow) ordinary hard disks.


  • Name: Rolf Fokkens
  • Email:
  • Release notes owner:

Current status

  • Targeted release: Fedora 20
  • Last updated: 2013-06-25
  • Tracker bug: <will be assigned by the Wrangler>

Detailed Description

Recent Linux kernels support the use of Solid State Drives as caches for rotational hard disks. Because the high cost per GB for SSD devices this feature may bring the best of both: fast end big yet affordable storage capacity. Linux kernel 3.9 introduced dm-cache, kernel 3.10 introduces bcache.

Benefit to Fedora


  • Proposal owners: Enable caching features in new kernels
  • Other developers: Support the caching features in their respective packages. Special focus should be on making the system boot from a cached root FS.
  • Release engineering: All packages should operate in close harmony te make this work. Only a rebuild of the relevant packages is required.
  • Policies and guidelines: No changes I think.

Upgrade/compatibility impact

N/A (not a System Wide Change)

How To Test

Implementing a caching root FS requires a reinstall for sure, because caching cannot be added to existing volumes!

Testing involves doing a clean install of Fedora, while configuring in anaconda a cached root FS. After the installation the cache state should be checked (if it is operational or not.

Additional tests:

  • run benchmarks (see performance improvement over non cached storage)
  • update the kernel (see if dracut builds a functional initramfs including caching
  • ...

User Experience

Users should experience improved storage performance.


Although the kernel supports SSD caching, the other mentioned packages should be changed to support this and make it really work.

Contingency Plan

  • Contingency mechanism: Revert the shipped configuration of the relevant packages.
  • Contingency deadline: beta freeze
  • Blocks release? No


N/A (not a System Wide Change)

Release Notes