Changes/SSD cache

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= SSDcache =
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= SSD cache =
  
 
== Summary ==
 
== Summary ==
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== Current status ==
 
== Current status ==
 
* Targeted release: [[Releases/20|Fedora 20]]  
 
* Targeted release: [[Releases/20|Fedora 20]]  
* Last updated: 2013-06-25
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* Last updated: 2013-07-08
 
<!-- After the change proposal is accepted by FESCo, tracking bug is created in Bugzilla and linked to this page  
 
<!-- After the change proposal is accepted by FESCo, tracking bug is created in Bugzilla and linked to this page  
 
Bugzilla states meaning as usual:
 
Bugzilla states meaning as usual:
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CLOSED as NEXTRELEASE -> change is completed and verified and will be delivered in next release under development
 
CLOSED as NEXTRELEASE -> change is completed and verified and will be delivered in next release under development
 
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* Tracker bug: <will be assigned by the Wrangler>
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* Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=998543 #998543]
  
 
== Detailed Description ==
 
== Detailed Description ==
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== Benefit to Fedora ==
 
== Benefit to Fedora ==
<!-- What is the benefit to the platform?  If this is a major capability update, what has changed?  If this is a new functionality, what capabilities does it bring? Why will Fedora become a better distribution or project because of this proposal?-->
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Fedora will support SSD's in a way that brings the speed of SSD's to the user, while also bringing the capacity of HDD's. The user however does not need to plan what data to put where (SSD or HDD): the Linux kernel will take care of that based on the usage patern.
  
 
== Scope ==
 
== Scope ==
<!-- What work do the developers have to accomplish to complete the change in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
 
  
* Proposal owners:  
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* Proposal owners: Enable caching features in new kernels
<!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
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* Other developers: N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Other developers: Support the caching features in their respective packages. Special focus should be on making the system boot from a cached root FS.
<!-- What work do other developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
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* Release engineering: N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Release engineering: All packages should operate in close harmony te make this work. Only a rebuild of the relevant packages is required.
<!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)?  Is a mass rebuid required?  If a rel-eng ticket exists, add a link here. -->
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* Policies and guidelines: N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Policies and guidelines: No changes I think.
<!-- Do the packaging guidelines or other documents need to be updated for this feature?  If so, does it need to happen before or after the implementation is done?  If a FPC ticket exists, add a link here. -->
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== Upgrade/compatibility impact ==
 
== Upgrade/compatibility impact ==
<!-- What happens to systems that have had a previous versions of Fedora installed and are updated to the version containing this change? Will anything require manual configuration or data migration? Will any existing functionality be no longer supported? -->
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Implementing a caching root FS using bcache requires a reinstall for sure, because bcache requires its own superblock on disks/volumes!
  
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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All existing Fedora functionality remains as is.
N/A (not a System Wide Change)
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== How To Test ==
 
== How To Test ==
<!-- This does not need to be a full-fledged document. Describe the dimensions of tests that this change implementation is expected to pass when it is done.  If it needs to be tested with different hardware or software configurations, indicate them. The more specific you can be, the better the community testing can be.  
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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.
  
Remember that you are writing this how to for interested testers to use to check out your change implementation - documenting what you do for testing is OK, but it's much better to document what *I* can do to test your change.
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Additional tests:
 
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* run benchmarks (see performance improvement over non cached storage)
A good "how to test" should answer these four questions:
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* update the kernel (see if dracut builds a functional initramfs including caching
 
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* ...
0. What special hardware / data / etc. is needed (if any)?
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1. How do I prepare my system to test this change? What packages
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need to be installed, config files edited, etc.?
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2. What specific actions do I perform to check that the change is
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working like it's supposed to?
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3. What are the expected results of those actions?
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-->
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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N/A (not a System Wide Change)
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== User Experience ==
 
== User Experience ==
<!-- If this change proposal is noticeable by its target audience, how will their experiences change as a result?  Describe what they will see or notice. -->
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Users should experience improved storage performance.
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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N/A (not a System Wide Change)
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== Dependencies ==
 
== Dependencies ==
<!-- What other packages (RPMs) depend on this package?  Are there changes outside the developers' control on which completion of this change depends?  In other words, completion of another change owned by someone else and might cause you to not be able to finish on time or that you would need to coordinate?  Other upstream projects like the kernel (if this is not a kernel change)? -->
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Although the kernel supports SSD caching, the other mentioned packages should be changed to support this and make it really work.
 
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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N/A (not a System Wide Change)
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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.  -->
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* Contingency mechanism: (What to do?  Who will do it?) N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* 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. -->
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* Contingency deadline: beta freeze
* Contingency deadline: N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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* Blocks release? No
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
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* Blocks release? N/A (not a System Wide Change), Yes/No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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== Documentation ==
 
== Documentation ==
<!-- Is there upstream documentation on this change, or notes you have written yourself?  Link to that material here so other interested developers can get involved. -->
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https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/device-mapper/cache.txt
  
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
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https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/bcache.txt
N/A (not a System Wide Change)
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 +
http://forums.gentoo.org/viewtopic-t-959542.html
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http://blog.kylemanna.com/linux/2013/06/30/ssd-caching-using-dmcache-tutorial/
  
 
== Release Notes ==
 
== Release Notes ==
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[[Category:ChangePageIncomplete]]
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[[Category:ChangeAcceptedF20]]
<!-- When your change proposal page is completed and ready for review and announcement -->
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<!-- remove Category:ChangePageIncomplete and change it to Category:ChangeReadyForWrangler -->
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<!-- The Wrangler announces the Change to the devel-announce list and changes the category to Category:ChangeAnnounced (no action required) -->
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<!-- After review, the Wrangler will move your page to Category:ChangeReadyForFesco... if it still needs more work it will move back to Category:ChangePageIncomplete-->
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<!-- Select proper category, default is Self Contained Change -->
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[[Category:SelfContainedChange]]
 
[[Category:SelfContainedChange]]
<!-- [[Category:SystemWideChange]] -->
 

Revision as of 13:49, 19 August 2013

Contents

SSD cache

Summary

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

Owner

  • Name: Rolf Fokkens
  • Email: rolf@rolffokkens.nl
  • Release notes owner:

Current status

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

Fedora will support SSD's in a way that brings the speed of SSD's to the user, while also bringing the capacity of HDD's. The user however does not need to plan what data to put where (SSD or HDD): the Linux kernel will take care of that based on the usage patern.

Scope

  • 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

Implementing a caching root FS using bcache requires a reinstall for sure, because bcache requires its own superblock on disks/volumes!

All existing Fedora functionality remains as is.

How To Test

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.

Dependencies

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

Documentation

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/device-mapper/cache.txt

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/bcache.txt

http://forums.gentoo.org/viewtopic-t-959542.html

http://blog.kylemanna.com/linux/2013/06/30/ssd-caching-using-dmcache-tutorial/

Release Notes