Hi guys! I would like to backup my DomUs via ftp. Unfortunately we don''t have LVM at this system. So I found this solution: xm sysrq xenvm1 s xm pause xenvm1 cp image /backup xm unpause xenvm1 Ok tis works. But now I wanted to test this backup. I copied the cfg and changed the MAC adress. I started the VM on the same Dom0 with xm create -c backup. The VM started correctly and changed the IP Settings. Now I got this error: SysRq : HELP : loglevel(0-9) reBoot Crash terminate-all-tasks(E) ... After a reboot the MySQL server is crashed. So is this the right way? Or what is my mistake? Best regards, Stefan _______________________________________________ Xen-users mailing list Xen-users@lists.xen.org http://lists.xen.org/xen-users
Am Donnerstag, 12. April 2012, 11:10:36 schrieb Stefan Becker:> I started the VM on the same Dom0 with xm create -c backup. The VM started > correctly and changed the IP Settings. Now I got this error: SysRq : HELP : > loglevel(0-9) reBoot Crash terminate-all-tasks(E) ...If i understand right you just "backup" the disk images - not the full system? This will result in a defect copy of your DomU. Not shure where you get the SysRQ error, but if i read right this is the result of your sysrq command before pausing the domu. The correct way would be to shutdown the DomU smoothly before copying it if you have no other option. Or did i miss something here? best regards, Niels. -- --- Niels Dettenbach Syndicat IT & Internet http://www.syndicat.com --- _______________________________________________ Xen-users mailing list Xen-users@lists.xen.org http://lists.xen.org/xen-users
I copy the disk, swap and cfg files.... What do you mean with full system? Ok but I ask me, why the author of the book writes this solutuion? Best regards Stefan -----Ursprüngliche Nachricht----- Von: xen-users-bounces@lists.xen.org [mailto:xen-users-bounces@lists.xen.org] Im Auftrag von Niels Dettenbach Gesendet: Donnerstag, 12. April 2012 11:30 An: xen-users@lists.xen.org Betreff: Re: [Xen-users] Backup a DomU Am Donnerstag, 12. April 2012, 11:10:36 schrieb Stefan Becker:> I started the VM on the same Dom0 with xm create -c backup. The VM > started correctly and changed the IP Settings. Now I got this error:SysRq : HELP :> loglevel(0-9) reBoot Crash terminate-all-tasks(E) ...If i understand right you just "backup" the disk images - not the full system? This will result in a defect copy of your DomU. Not shure where you get the SysRQ error, but if i read right this is the result of your sysrq command before pausing the domu. The correct way would be to shutdown the DomU smoothly before copying it if you have no other option. Or did i miss something here? best regards, Niels. -- --- Niels Dettenbach Syndicat IT & Internet http://www.syndicat.com ---
Am Donnerstag, 12. April 2012, 11:43:13 schrieb Stefan Becker:> I copy the disk, swap and cfg files.... What do you mean with full system?If you just pause a VM you did not have any dates from the memory. Firing a sysrq s did do a "sync" to the discs but as the filesystems are not cleanly umounted, filehandles are closed and processes are hung up your system could not understand as "completely consistent". You just "hope" that everything it''s on his place when you copy it... Depending from the load of your system and the time between sysrq s and vm pause disk content would be differ more or less too. I do not know the book but from my understanding this is a ugly hack which may work - but not a real solution... In such cases it may much more sense to use any simple but working backup utility like dump / restore. Handling with MySQL databases requires to use something like mysqldump or cleanly shutting down MySQL as MySQL uses it''s own technologies for caching and buffering beside the OS ones... hth best regards, Niels. -- --- Niels Dettenbach Syndicat IT & Internet http://www.syndicat.com --- _______________________________________________ Xen-users mailing list Xen-users@lists.xen.org http://lists.xen.org/xen-users
Stefan Becker wrote:>I copy the disk, swap and cfg files.... What do you mean with full system?"full system" would mean the entire guest - not just the filesystem images, but the machine state as well (which means the entire memory image plus processor state). When you backup the disk image files, what you are getting is roughly the same as you''d have on the disks of a bare-metal machine after yanking the power cord ! Just telling the OS to sync is **NOT** enough in the general case - that will only sync data which applications have asked the OS to write to disk, anything cached by the application (particularly the case with databases) will not be included. I agree with Niels, it''s an ugly way to do it which relies on taking a dirty snapshot of the filesystem and hoping that it will clean up when the guest boots with it. It''s a topic that comes up every now and then (try searching the archives), and there are many points of view. Personally, I treat each guest as a machine in it''s own right and back it up from within the guest in exactly the same way as I handle a bare-metal machine.>Ok but I ask me, why the author of the book writes this solutuion?No idea, you haven''t given any clue what book you''ve been reading. It''s a method that will "work well enough" for some use cases - typically low write frequency/volume, no applications which cache data, "robust" filesystems. Ignore these provisos and it gets less reliable, and in extreme can be virtually guaranteed to result in corrupt data for some use cases. The author should have pointed out these limitations. -- Simon Hobson Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed author Gladys Hobson. Novels - poetry - short stories - ideal as Christmas stocking fillers. Some available as e-books.