From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51750) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UZyvI-0005Cw-0i for qemu-devel@nongnu.org; Wed, 08 May 2013 03:36:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UZyvD-0005sl-PG for qemu-devel@nongnu.org; Wed, 08 May 2013 03:36:23 -0400 Received: from [222.73.24.84] (port=12377 helo=song.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UZyvD-0005ru-Df for qemu-devel@nongnu.org; Wed, 08 May 2013 03:36:19 -0400 Message-ID: <5189FFEF.3080202@cn.fujitsu.com> Date: Wed, 08 May 2013 15:34:07 +0800 From: yuxh MIME-Version: 1.0 References: <5189E019.1090702@cn.fujitsu.com> <20130508063656.GA2766@fam-laptop.nay.redhat.com> In-Reply-To: <20130508063656.GA2766@fam-laptop.nay.redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] qemu-img problem when create a file larger than fs's size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: qemu-devel@nongnu.org Thank you for your reply. I agreed what you said. And do you think we shall print a prompt to user when the size user=20 specified is larger than available space ? On 05/08/2013 02:36 PM, Fam Zheng wrote: > I think it's the system admin to be responsible for the risk of over > provisioning. We have host sparse file[1] (as your example) for > preallocated image (for example, -f raw), as well as sparse image (as > supported in qcow2, vmdk, etc.). There are cases that host file system > is extended or the vm disk is moved to a larger storage when the actual > data grows closer to full, so it's not very practical to limit the > creating size, just as this is quietly valid in linux, no matter how > small your /tmp is. > > # df /tmp/ -h > Filesystem Size Used Avail Use% Mounted on > tmpfs 3.8G 14M 3.8G 1% /tmp > # touch /tmp/a > # truncate /tmp/a --size 10000T > # ls -l /tmp/a > -rw-rw-r--. 1 fam fam 10995116277760000 May 8 14:33 /tmp/a > > [1]: http://en.wikipedia.org/wiki/Sparse=5Ffile > > On Wed, 05/08 13:18, yuxh wrote: >> Hello all, >> >> I have to consult you a qemu-img's problem. >> >> Is this reasonable to create a file which is larger than the >> available size of the fs by qemu-img cmd ? >> >> When I use qemu-img create a file which is larger than the available >> size of the fs, the creation is completed succesfully. >> >> However when I use this file in guest as a guest's disk, and write >> beyond the size the host file can provides, the guest was paused by >> qemu-kvm or libvirt and was in maybe a infinite circle where the >> guest just can't be used except I detach the disk from guest or >> destroy the guest. >> >> I read the qemu-img's code and found it just create the file as we >> required and doesn't check if the size we specify is reasonable.But >> this may let the guest in a risk of meeting the problem I describe >> above. >> >> Exp: >> [root@build mytest]# df -ah /mytest/ >> Filesystem Size Used Avail Use% Mounted on >> /dev/sdb2 2.0G 3.1M 1.9G 1% /mytest >> [root@build mytest]# qemu-img create -f raw test.raw 3G >> Formatting 'test.raw', fmt=3Draw size=3D3221225472 >> [root@build mytest]# ls -l test.raw >> -rw-r--r--. 1 root root 3221225472 May 8 12:23 test.raw >> [root@build mytest]# >> >> Thank you. >> >> Best Regards >> Xinghai Yu >> > --=20 =E4=BB=A5=E4=B8=8A =E7=AC=AC=E4=B8=80=E8=BD=AF=E4=BB=B6=E4=BA=8B=E4=B8=9A=E9=83=A8 =E7=AC=AC= =E4=B8=80=E5=BC=80=E5=8F=91=E9=83=A8 driver=E7=BB=84 =E4=BA=8E=E6=98=9F=E6= =B5=B7 Best Regards -------------------------------------------------- Yu Xinghai Development Dept.I Nanjing Fujitsu Nanda Software Tech. Co., Ltd.(FNST) No.6 Wenzhu Road, Nanjing, 210012, China TEL: +86+25-86630566-8533 FUJITSU INTERNAL: 7998-8533 FAX: +86+25-83317685 MAIL: yuxinghai@cn.fujitsu.com -------------------------------------------------- =