From: "Wang, Wei W" <wei.w.wang@intel.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: "lersek@redhat.com" <lersek@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"qemu-block@nongnu.org" <qemu-block@nongnu.org>,
"mreitz@redhat.com" <mreitz@redhat.com>
Subject: RE: Question on Compression for Raw Image
Date: Tue, 20 Oct 2020 14:22:43 +0000 [thread overview]
Message-ID: <6124d55766e4477299a5796a002276a0@intel.com> (raw)
In-Reply-To: <20201020080051.GA4452@merkur.fritz.box>
On Tuesday, October 20, 2020 4:01 PM, Kevin Wolf wrote:
> Am 20.10.2020 um 03:31 hat Wang, Wei W geschrieben:
> > Hi,
> >
> > Does anyone know the reason why raw-format.c doesn't have
> compression
> > support (but qcow has the supported added)? For example, raw image
> > backup with compression, "qemu-img convert -c -O raw origin.img
> > dist.img", doesn't work.
>
> A raw image is by definition a file that contains the exact same sequence of
> bytes as the guest sees, without any additional information or encoding. If
> you compress a raw file, the guest will see compressed data on its hard disk
> instead of the real data.
Ok, thanks. I'm thinking QEMU could do decompression of the compressed data in raw.img when guest reads data.
>
> Anything you could do to add transparent compression to it would mean that
> it's not a raw image any more, but a new image format.
>
Yes, decompression makes it transparent to the guest. Would you think it's good to reuse the raw image implementation, just add the compress/decompress option?
Thanks,
Wei
next prev parent reply other threads:[~2020-10-20 14:24 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 1:31 Question on Compression for Raw Image Wang, Wei W
2020-10-20 8:00 ` Kevin Wolf
2020-10-20 14:22 ` Wang, Wei W [this message]
2020-10-20 14:32 ` Eric Blake
2020-10-20 14:42 ` Richard W.M. Jones
2020-10-20 14:49 ` Alberto Garcia
2020-10-20 14:36 ` Alberto Garcia
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