"dd" is _the_ absolute worst option for backups. It is stupid, has no concept of data integrity, and is stupid. And the default conv options are appalling - and it's stunningly stupid.
Great for image copies in failure/forensic situations, other than that it's downright ... er, see above. [f]sync doesn't really help a lot in this situation either - from a Linux perspective. Last I looked (on a non-z system), fsync doesn't guarantee the (physical) I/O actually gets written then-and-there. Linux has I/O schedulers in play, and then there is pdflush/BDI to worry about waking up. Sometime, somewhere the I/O does get flushed. Blktrace has been around for a while now - the (timimg) output makes for interesting reading. Then we have z/VM snoozing away in the corner ... Sebastian and his cohorts can fill you in there. If it (ever) worked you were IMHO lucky. I'd be slipping some (long) sleeps in your scripts. Shane ... On Tue, 23 Nov 2010 10:51:53 +0100 Sebastian Ott wrote: > > 2. Problem: > > > > Because I lack the FLASHCOPY function I use for disk to disk copy > > dd. > > > > dd bs=4096 if=/dev/dasdx of=/dev/dasdy > > > > In principle it works ok. But when I do a chccwdev -d 0.0.xxxx even > > with an udevadm settle --timeout=20 afterwards, > > the file system gets corrupted, when I attach it to another guest. > > > > I am really lost since all that was working well under SLES 10 SP2. > > I would really like to know if someone had similar experience in > > SLES 11 SP1. > > The data is not guaranteed to be written in this case. This is due to > changes in the linux block layer (it was not guaranteed to be written > in sles 10 either but worked by chance). > You have 2 options here: > * tell dd to sync its data (check the man page - i think the option is > fsync) > * manually run "sync" after dd returns ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
