On Fri, Oct 24, 2008 at 03:16:30AM +0200, Carlo Wood wrote: > Hiya, don't know where else to report this. Please > correct me if this isn't the right place. > > I just ran into a serious bug :(( > > We were trying to create a virtual filesystem > in an image (file) of around 238 GB. [Using double losetup configuration] > > Here the machine completely halted/crashed. I don't know what > happened, because it's a remote machine. > > The writing of the inode table started very fast, but it was > already slowing down the last few - and completely stopped > at 306, which was 12 minutes ago (my ssh connection to the > machine still didn't time out, weird enough). That's a classic case of mke2fs tickling a VM bug. The VM should be able to do proper write throttling, but mke2fs writes a blocks very quickly, and so it's a great test of the kernel virtual memory subsystem. :-) So the fact that your system hung is a kernel bug, probably caued by the double /dev/loop configuration. What version of the kernel are you using? There is a workaround that might help: "export MKE2FS_SYNC=10". This will force an explicit sync system call every 10 blockgroups, which tends to work around the kernel VM bug. It's not the default mainly because mke2fs is such a great kernel test tool, and the VM really needs to be able to handle this case. > Note that mke2fs says: 29097984 inodes, 58195960 blocks > That is 58195960 * 4096 = 238370652160 the full size of > the image file?!? > > This partition is only 200MB though! That's because you created /dev/loop1 as a loop device with an offset of 512*63 bytes from the beginning of /dev/loop0. There is no way to set the maximum size of a loop device (it's not something which is currently defined as part of the interface of the LOOP_SET_STATUS ioctl. If you want to do things manually like this, you'll need to explicitly specify the size of the desired filesystem to mke2fs; it's a shortcoming in the loop device. The other way to do things would be to create an image file of the desired partition length, and then assemble it by hand afterwards; sorry, the loop device wasn't designed to be used to emulate a partitioned disk. It could be, but kernel patches would be required to extend its functionality. Regards, - Ted _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
