>>> Joachim <dav.pin...@gmail.com> schrieb am 06.07.2011 um 18:45 in Nachricht
> Hello,
> I am currently trying to implement an iscsi target driver for a remote
> storage space with tgt.
> At first, the driver was slow (quite normal), but worked quite well,
> with a testing script i wrote.
> Then, I added some features for it to get faster, and thus the problem
> appeared.
> Actually, after the login to the target with iscsiadm, I partition the
> disk, create some filesystem, and then make a copy of a random file
> tree, before umounting the partition, and logout.
> When i try to mount the partition again (after all required
> manipulations with iscsiadm), i stumble upon a series of IO Errors,
> meaning that my filesystem is totally corrupted, and that some of the
> data weren't saved by my driver (be it that i didnt receive it or that
> i could not save it)
> When I use the sync command before umounting, I actually succeed to
> read the whole file system again afterwards.

Usually "umount" should sync that filesystem's data, and probably wait until 
that finished. I don't thin that iSCSI adds another buffering layer that could 
hold back data between unmount and iSCSI logout.


> While searching a solution, I found this in another thread of this
> mailing list (http://groups.google.com/group/open-iscsi/browse_thread/ 
> thread/e445471fab2af459/b8fae3dfb6e6c68f?pli=1) :
> >>   is the Sync cache that occurs at logout actually sending data? or is
> >> it just sending a scsi msg to flush/checkpoint the target side?
> >
> >No data. It is just telling the target side to basically flush what it
> >has in its cache. For example tgt does a sync() to write out data to the
> >backing store. I believe  IET does the equivalent of a sync() but it is
> >done from the kernel since IET is implemented there. Look at the source
> >for IET or just fire off a mail to that list if you want to know all the
> >details of what it does.
> If i'm not misunderstanding what's written here, That means that when
> i type the command
> $ iscsiadm --mode node --targetname mytarget --logout
> All that is done is actually sending a sync command to the target (tgt
> in my case) without sending any data relating to the system/iscsid
> cache ?
> My hypothesis is thus that my problem originates from this behavior of
> the iscsiadm logout action. If I'm not wrong about that, how can i
> make it so that a synchronization is done before the iscsi logout ? Or
> I am completely wrong, and then do you have any insight as to what my
> problem really is ?
> Thanks for your help in advance !


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