And what of "writeback" and "writethough"

[tbielawa]

With respect to: disk IO modes in QEMU/KVM

[tbielawa]

Training last week provided some insight on this topic.

• Write-back is 'lossy' (dirty pages aren't flushed immediately)
• Write-through is more disk intensive

How to decide which caching mechanism is right for you? A major factor is considering how expensive your data is to get back. Go with write-back for a performance boost if data integrity isn't your top concern. Go with write-through if you need changes to be flushed asap.

There's some other stuff to consider as well. Such as: virsh defaults and auto-detection, how they're based off of virtual disk formats.

[tbielawa]

Notes:

• Optimizing the QEMU Storage Stack - http://www.linuxplumbersconf.org/2010/ocw/system/presentations/651/original/Optimizing_the_QEMU_Storage_Stack.pdf
• Kernel Asynchronous I/O (AIO) Support for Linux - http://lse.sourceforge.net/io/aio.html

[tbielawa]

• https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Tuning_and_Optimization_Guide/chap-Virtualization_Tuning_Optimization_Guide-BlockIO.html

writethrough and writeback