Dafault caching policy

a GUI for virtual machines using QEMU as the backend

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#20 Dafault caching policy

Milestone: Next Release

Status: closed

Owner: nobody

Labels: Other (4)

Priority: 5

Updated: 2016-06-01

Created: 2011-12-05

Creator: Anonymous

Private: No

The default caching policy should be 'writeback' since 'writethrough' is very slow.

Or maybe it could be 'unsafe' when it is not longer unsafe to use it.

Any thoughts on this?

Discussion

Andrey Rijov - 2011-12-11

You are talking about QEMU or AQEMU?
In AQEMU on storage device settings caching policy not assigned by default.
Do you offer always send "writeback" option to QEMU that it used instead of the default?

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Andrey Rijov - 2011-12-11

labels: --> Other

milestone: --> Next Release
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Nobody/Anonymous - 2011-12-12

i'm talking about aqemu.

What ever default is assigned to (witethrough?) it should be writeback (don't know who handles the default alias).

In case of adding a storage to an vm i always had to change the cache option.
I think it would be better if the default is an more useful one. Useful with the meaning of time consuming and data integrety.

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Tobias Gläßer - 2016-06-01

status: open --> closed
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Tobias Gläßer - 2016-06-01

Here's a quote from the qemu 2.6 man page:

By default, the cache=writeback mode is used. It will report data writes as completed as soon as
the data is present in the host page cache. This is safe as long as your guest OS makes sure to
correctly flush disk caches where needed. If your guest OS does not handle volatile disk write
caches correctly and your host crashes or loses power, then the guest may experience data
corruption.

Since cache=writeback is the default in the latest qemu, I think I can close this.

If you have any other issues, https://github.com/tobimensch/aqemu/issues is now
the recommended place to file them.

AQEMU version 0.9.2 was released yesterday.

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