Sunday 13th of October: Fedora bcache test day
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Hi All,
Bcache-tools for Fedora 20 is now close to completion, so it's integrated very well with dracut, udev, util-linux and lvm2. What's left is some good testing :-)
To do some testing there's a Fedora SSD Cache is this sunday October 13th 2013. This Fedora Test Day will focus on bcache based SSD Caching in Fedora 20:
https://fedoraproject.org/wiki/Test_Day:2013-10-13_SSD_Cache
If you're interested in trying out the bcache SSD caching functionality on Fedora, step by step instructions are available for:
- bcache on physical hardware
- bcache in a virtual machine
- non-root FS on bcache (with or without LVM)
- root FS on bcache (wtih or without LVM)
The objective of this Test day is to demonstrate a working Fedora 20 system using bcache. Te be more specific:
* The system boots OK; after booting bcache is operating as expected
* The system updates ("yum update") OK. After updating specifically the kernel the system boots OK.
* The system is bootable when the caching device is disabled.
Although testing on real hardware is closest to "the real thing", testing in a VM may also provide good insights on the proper working of bcache (except for performance) in relation to the other software.
If you do plan on showing up to the test day pop into #fedora-test-day on freenode and give us a shout! If you can't make the date of the test day, adding test case results to the wiki anytime next week is fine as well.
The Wiki page is still under development, so expect some improvements before sunday.
Rolf Fokkens
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Re: bcache strategies for consistency in case of powerloss
Hi Florian,
Quoted 9 lines · Florian Weimer
Quoted 5 lines · Rolf Fokkens
Quoted 3 lines · Florian Weimer
Is there a write-up somewhere documenting what strategies are implemented by bcache to keep the SSD and the hard disk contents in sync even in the event of a sudden power loss?
This is good place to start: http://bcache.evilpiepirate.org/
It doesn't actually address this as far as I can see. It only describes how the data structure integrity is maintained on the SSD side. Even that doesn't seem to address torn writes (which are problem for cheap-to-medium-grade SSDs). The code contains "propagate barriers" as a to-do item (see the beginning of
drivers/md/bcache/btree.c). I couldn't find anything that discusses write ordering issues which can occur in write-through mode.
I don't have the expertise myself to answer your question, so I hereby forward this question to Kent and Gabriel and the bcache mail list.
Rolf
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