On Wed, 05/08 15:34, yuxh wrote: > > 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 > specified is larger than available space ?
Might be nice, but it's hard to define "available space", and "available space" at creating time promises nothing. Even if the user creates a small image which seems safe, risk is still there: when other applications' data fills up the "available space", the use still experiences the same problem. > > 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_file > > > >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=raw size=3221225472 > >>[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 > >> > > > > -- > 以上 > > 第一软件事业部 第一开发部 driver组 于星海 > 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: yuxing...@cn.fujitsu.com > -------------------------------------------------- -- Fam