Changes/SSD cache

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= SSD cache =
+
= SSD cache (bcache) =
 +
This page originally covered SSD caching in general targeted for Fedora 20, including both dm-cache and bcache. In the processes it became clear that introducing basic bcache support was feasable for Fedora 20 and dm-cache had te be postponed until later.
  
 
== Summary ==
 
== Summary ==
Using recent kernel (3.9 and later) features for (fast) SSD caching of (slow) ordinary hard disks. Currently two kinds of SSD caching are available in the Linux kernel: bcache and dm-cache. In Fedora 20 basic bcache support is provided by the "bcache-tools" package, this page now provides suggestions on how to move forward in Fedora 21.
+
Using recent kernel (3.9 and later) features for (fast) SSD caching of (slow) ordinary hard disks. Currently two kinds of SSD caching are available in the Linux kernel: bcache and dm-cache. In Fedora 20 basic bcache support is provided by the "bcache-tools" package, with small changes in util-linux, dracut and lvm2 as well. This page now provides suggestions on how to move forward in Fedora 22.
  
The main suggestion is to implement bcache support in Anaconda, which allows easy installation of Fedora on "bcached" root-FS.
+
The Change described on this page is to implement bcache support in Anaconda, which allows easy installation of Fedora on "bcached" root-FS and support for existing (root or non-root) bcache partitions during Fedora installation.
  
 
Moving forward with dm-cache is not covered by this page, because the LVM team already plans to integrate dm-cache support in LVM2. See http://www.redhat.com/archives/dm-devel/2014-January/msg00072.html
 
Moving forward with dm-cache is not covered by this page, because the LVM team already plans to integrate dm-cache support in LVM2. See http://www.redhat.com/archives/dm-devel/2014-January/msg00072.html
  
== Owner ==
+
== Owners ==
  
 
* Name: [[User:rolffokkens|Rolf Fokkens]]
 
* Name: [[User:rolffokkens|Rolf Fokkens]]
 
* Email: rolf@rolffokkens.nl
 
* Email: rolf@rolffokkens.nl
 +
* Name: [[User:dlehman|Dave Lehman]]
 +
* Email: dlehman AT fedoraproject
 
* Release notes owner: <!--- To be assigned by docs team [[User:FASAccountName| Release notes owner name]] <email address> -->
 
* Release notes owner: <!--- To be assigned by docs team [[User:FASAccountName| Release notes owner name]] <email address> -->
 
<!--- UNCOMMENT only for Changes with assigned Shepherd (by FESCo)
 
<!--- UNCOMMENT only for Changes with assigned Shepherd (by FESCo)
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== Current status ==
 
== Current status ==
* Targeted release: [[Releases/21|Fedora 21]]  
+
* Targeted release: [[Releases/22|Fedora 22]]  
 
* Last updated: 2014-03-16
 
* Last updated: 2014-03-16
 
<!-- 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  
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== Detailed Description ==
 
== 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.
 
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.
 +
 +
The introduction of bcache-tools in Fedora 20, and minor changes to util-linux, dracut and lvm2 allowed users to create SSD-cached block devices on which they could create bcache filesystems and/or LVM volumes. Creating a bcache root FS is possible using bcache-tools, but complicated because bcache requires a "fresh" block device destroying all data currently on it. Solving this involves adding bcache support in Anaconda. This covers both support for "manually created" (bcache-tools) bcached filesystems, and support for creating a bcached root FS. (Implementing bcache support in Anaconda can't be done by me, and needs to be done by the Anaconda team, hence I consider this a suggestion. Discussions on this topic with dlehman indicated an estimated effort of 1-2 weeks to implement).
 +
 +
 +
Moving forward with dm-cache is not covered by this page because the LVM team already plans to integrate dm-cache support in LVM2. See http://www.redhat.com/archives/dm-devel/2014-January/msg00072.html. It should be noted that (in contrast to bcache) dm-cache support may not require Anaconda changes because it'll be an integral part of lvm2.
 +
 +
Related Bugzilla's:
 +
* https://bugzilla.redhat.com/show_bug.cgi?id=1003208
 +
* https://bugzilla.redhat.com/show_bug.cgi?id=1019442
  
 
== Benefit to Fedora ==
 
== 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.
+
The availability of bcache-tools in Fedora 20 already brought the speed of SSD's to Fedora users, while also bringing the capacity of HDD's. This was limited however to expert Fedora users who feel comfortable using te command line.
 +
 
 +
The SSD caching support in Fedora 20 will become available to more Fedora users when Anaconda will support this in Fedora 22.
  
 
== Scope ==
 
== Scope ==
  
* Proposal owners: Enable caching features in new kernels
+
* Proposal owners: build and test blocks package (or include blocks in bcache-tools), support Anaconda team when needed, test Anaconda.
  
* Other developers: Support the caching features in their respective packages. Special focus should be on making the system boot from a cached root FS.
+
* Other developers: Build bcache support in Anaconda (by Anaconda team)
  
* Release engineering: All packages should operate in close harmony to make this work. Only a rebuild of the relevant packages is required.
+
* Release engineering:  
  
* Policies and guidelines: No changes I think.
+
* Policies and guidelines:
  
 
== Upgrade/compatibility impact ==
 
== 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.
 
All existing Fedora functionality remains as is.
  
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== User Experience ==
 
== User Experience ==
Users should experience improved storage performance.
+
Users should experience improved storage performance after easy installation of Fedora in bcache devices.
  
 
== Dependencies ==
 
== Dependencies ==
Although the kernel supports SSD caching, the other mentioned packages should be changed to support this and make it really work.
+
Anaconda will depend on bcache tools
  
 
== Contingency Plan ==
 
== Contingency Plan ==
  
* Contingency mechanism: Revert the shipped configuration of the relevant packages.
+
* Contingency mechanism: Revert bcache changes in Anaconda, revoke the blocks package.
 
* Contingency deadline: beta freeze
 
* Contingency deadline: beta freeze
 
* Blocks release? No
 
* Blocks release? No
  
 
== Documentation ==
 
== 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
 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/bcache.txt
  
http://forums.gentoo.org/viewtopic-t-959542.html
+
https://github.com/g2p/bcache-tools
 
+
http://blog.kylemanna.com/linux/2013/06/30/ssd-caching-using-dmcache-tutorial/
+
  
 
== Release Notes ==
 
== Release Notes ==
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[[Category:ChangePageIncomplete]]
 
[[Category:ChangePageIncomplete]]
[[Category:SystemWideChange]]
+
[[Category:SelfContainedChange]]

Latest revision as of 19:40, 9 April 2014

Contents

[edit] SSD cache (bcache)

This page originally covered SSD caching in general targeted for Fedora 20, including both dm-cache and bcache. In the processes it became clear that introducing basic bcache support was feasable for Fedora 20 and dm-cache had te be postponed until later.

[edit] Summary

Using recent kernel (3.9 and later) features for (fast) SSD caching of (slow) ordinary hard disks. Currently two kinds of SSD caching are available in the Linux kernel: bcache and dm-cache. In Fedora 20 basic bcache support is provided by the "bcache-tools" package, with small changes in util-linux, dracut and lvm2 as well. This page now provides suggestions on how to move forward in Fedora 22.

The Change described on this page is to implement bcache support in Anaconda, which allows easy installation of Fedora on "bcached" root-FS and support for existing (root or non-root) bcache partitions during Fedora installation.

Moving forward with dm-cache is not covered by this page, because the LVM team already plans to integrate dm-cache support in LVM2. See http://www.redhat.com/archives/dm-devel/2014-January/msg00072.html

[edit] Owners

  • Name: Rolf Fokkens
  • Email: rolf@rolffokkens.nl
  • Name: Dave Lehman
  • Email: dlehman AT fedoraproject
  • Release notes owner:

[edit] Current status

[edit] 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.

The introduction of bcache-tools in Fedora 20, and minor changes to util-linux, dracut and lvm2 allowed users to create SSD-cached block devices on which they could create bcache filesystems and/or LVM volumes. Creating a bcache root FS is possible using bcache-tools, but complicated because bcache requires a "fresh" block device destroying all data currently on it. Solving this involves adding bcache support in Anaconda. This covers both support for "manually created" (bcache-tools) bcached filesystems, and support for creating a bcached root FS. (Implementing bcache support in Anaconda can't be done by me, and needs to be done by the Anaconda team, hence I consider this a suggestion. Discussions on this topic with dlehman indicated an estimated effort of 1-2 weeks to implement).


Moving forward with dm-cache is not covered by this page because the LVM team already plans to integrate dm-cache support in LVM2. See http://www.redhat.com/archives/dm-devel/2014-January/msg00072.html. It should be noted that (in contrast to bcache) dm-cache support may not require Anaconda changes because it'll be an integral part of lvm2.

Related Bugzilla's:

[edit] Benefit to Fedora

The availability of bcache-tools in Fedora 20 already brought the speed of SSD's to Fedora users, while also bringing the capacity of HDD's. This was limited however to expert Fedora users who feel comfortable using te command line.

The SSD caching support in Fedora 20 will become available to more Fedora users when Anaconda will support this in Fedora 22.

[edit] Scope

  • Proposal owners: build and test blocks package (or include blocks in bcache-tools), support Anaconda team when needed, test Anaconda.
  • Other developers: Build bcache support in Anaconda (by Anaconda team)
  • Release engineering:
  • Policies and guidelines:

[edit] Upgrade/compatibility impact

All existing Fedora functionality remains as is.

[edit] 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
  • ...

[edit] User Experience

Users should experience improved storage performance after easy installation of Fedora in bcache devices.

[edit] Dependencies

Anaconda will depend on bcache tools

[edit] Contingency Plan

  • Contingency mechanism: Revert bcache changes in Anaconda, revoke the blocks package.
  • Contingency deadline: beta freeze
  • Blocks release? No

[edit] Documentation

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

https://github.com/g2p/bcache-tools

[edit] Release Notes