On Monday 20 March 2006 11:10, Alan Brown wrote: > On Fri, 17 Mar 2006, Wolfgang Denk wrote: > > Most critical options are: MT_ST_BUFFER_WRITES, MT_ST_ASYNC_WRITES, > > MT_ST_READ_AHEAD. Especially the combination of MT_ST_BUFFER_WRITES > > and MT_ST_ASYNC_WRITES prevents any way to reliably handle end of > > tape conditions. > > I thought Bacula tried to workaround this by backspacing and then reading > the last few blocks to see what got sucessfully written.
Unfortunately, what Bacula does (as you point out) is not exactly a workaround, but rather an attempt to verify afterwards, and there are a lot of drives that do not support a backspace record, so there are cases where Bacula cannot verify. Buffering writes can cause the tape drive to lag behind what Bacula writes and thus possibly overrun the end of the tape; async write means that Bacula might not know about an I/O error until *much* later, which is a catastrophic situation for backup. Read ahead shouldn't be a big problem providing that the SCSI drive is sufficiently intelligent to handle exceptions ... > > I have not had problems on our setup (yet), but I need to know if there's > a risk.... > > AB > > > > ------------------------------------------------------- > This SF.Net email is sponsored by xPML, a groundbreaking scripting language > that extends applications into web and mobile media. Attend the live > webcast and join the prime developer group breaking into this new coding > territory! > http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 > _______________________________________________ > Bacula-users mailing list > Bacula-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/bacula-users -- Best regards, Kern ("> /\ V_V ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
