Offset (2)
Hi, Under aix, we have several Informix databases which were created without offset in their dbspaces. The dbspaces are raw devices. We observed that the first bytes of some of these dbspaces were overwritten by aix for the lvcb (logical volume control block). Does someone know what can be the consequences of the overwritten? To introduce an offset in the dbspaces, does it exist a method other than backup and restore? -- Marcel Nihon -------------------------------------------------------------------- Service General d'Informatique (SEGI) Support logiciels Universite de Liege Sart Tilman B26 Tel. : +32(4)366.49.78 4000 Liege Fax : +32(4)366.29.20 Belgium email: Marcel.Nihon@ulg.ac.be
Be careful, I've had the database corrupted by this problem before during a reboot. I always offset at least 4K with AIX, even with raw devices. Gary Marcel Nihon wrote in message <36D282E8.D80DEDED@ulg.ac.be>... >Hi, >Under aix, we have several Informix databases which were created without >offset in their dbspaces. >The dbspaces are raw devices. >We observed that the first bytes of some of these dbspaces were >overwritten by aix for the lvcb >(logical volume control block).
Marcel Nihon wrote: > Hi, > Under aix, we have several Informix databases which were created without > offset in their dbspaces. > The dbspaces are raw devices. > We observed that the first bytes of some of these dbspaces were > overwritten by aix for the lvcb > (logical volume control block). > Does someone know what can be the consequences of the overwritten? > To introduce an offset in the dbspaces, does it exist a method other > than backup and restore? > > -- > Marcel Nihon > > -------------------------------------------------------------------- > Service General d'Informatique (SEGI) Support logiciels > Universite de Liege > Sart Tilman B26 Tel. : +32(4)366.49.78 > 4000 Liege Fax : +32(4)366.29.20 > Belgium email: Marcel.Nihon@ulg.ac.be Hi, this concerns the first 512 bytes of the logical volume. Some peple say: "Try to restore the DB from a backup. If it works then you won't have problems in the future." I do not believe this. I think that when you do some changes on the logical volume (adding or removing copies etc.) AIX might eventually write something to the (destroyed) LVCB. However, it is strongly recommended to specify an offset with every dbspace. 4k is enough as the LVCB is only 512 bytes. Regards - Helmut Leininger Bull AG / Vienna Unix Support Email: h.leininger@bull.at helmut.leininger@bull.net This opinion is mine and not necessarily that of my employer. No guarantees whatsoever.