From: Kaveh Razavi <kaveh@cs.vu.nl>
To: Alex Bligh <alex@alex.org.uk>
Cc: Kevin Wolf <kwolf@redhat.com>,
qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] Introduce cache images for the QCOW2 format
Date: Wed, 14 Aug 2013 15:37:30 +0200 [thread overview]
Message-ID: <520B881A.8080101@cs.vu.nl> (raw)
In-Reply-To: <962306F5-8851-498D-A629-C0BC59AD3758@alex.org.uk>
On 08/14/2013 01:57 PM, Alex Bligh wrote:
> I don't agree. The penalty for a qcow2 suffering a false positive on
> a change to a backing file is that the VM can no longer boot. The
> penalty for your cache suffering a false positive is that the
> VM boots marginally slower. Moreover, it is expected behaviour that
> you CAN change a backing file if there are no r/w images based on
> it. Your cache changes that assumption.
That is right. So when there is a change in the backing file, either the
cache should be invalidated or the changes should be propagated to the
cache image. If changes to the backing image are not frequent, then
invalidation is the simpler approach. In any case, there should be a
mechanism to detect this. I assume it is also undesirable for a VM to
see stale data when booting from a cow image twice.
Kaveh
next prev parent reply other threads:[~2013-08-14 13:37 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-13 17:03 [Qemu-devel] [PATCH] Introduce cache images for the QCOW2 format Kaveh Razavi
2013-08-13 21:37 ` Eric Blake
2013-08-14 11:13 ` Kaveh Razavi
2013-08-13 22:53 ` Alex Bligh
2013-08-14 11:28 ` Kaveh Razavi
2013-08-14 11:52 ` Fam Zheng
2013-08-14 12:03 ` Alex Bligh
2013-08-14 15:58 ` Richard W.M. Jones
2013-08-15 0:53 ` Fam Zheng
2013-08-15 5:51 ` Alex Bligh
2013-08-14 11:57 ` Alex Bligh
2013-08-14 13:37 ` Kaveh Razavi [this message]
2013-08-13 23:16 ` Alex Bligh
2013-08-14 11:42 ` Kaveh Razavi
2013-08-14 12:02 ` Alex Bligh
2013-08-14 13:43 ` Kaveh Razavi
2013-08-14 13:50 ` Alex Bligh
2013-08-14 14:26 ` Kaveh Razavi
2013-08-14 15:02 ` Alex Bligh
2013-08-14 15:32 ` Kevin Wolf
2013-08-15 7:50 ` Wenchao Xia
2013-08-15 8:11 ` Stefan Hajnoczi
2013-08-14 9:29 ` Stefan Hajnoczi
2013-08-14 14:20 ` Kaveh Razavi
2013-08-15 8:32 ` Stefan Hajnoczi
2013-08-15 12:25 ` Kaveh Razavi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=520B881A.8080101@cs.vu.nl \
--to=kaveh@cs.vu.nl \
--cc=alex@alex.org.uk \
--cc=kwolf@redhat.com \
--cc=qemu-devel@nongnu.org \
--cc=stefanha@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.