Should I use offset on first disk partitions ???

Hello Many people say that we must use offset when creating a dbspace/chunk located on the first partition of a physical disk, due to problems that may occur with the disk identification area (magic number). This number could be overwrited, and then the disk could be lost. What is the true in all this ?? I had this problem on a Sun machine about 2 years ago. We defined a raw device with the same size of the disk (2Gb) and created a dbspace with the same size, and every time the system was rebooted, the dbspace was lost. The problem was solved by defining a small partition of disk just to the magic number, and the rest of the disk to the raw device. Some time after this, Informix Techinical Support told me that we must always use offset when creating the rootdbspace, and without this we certainly would have this problem. I've seen many other Sun machines, and many other machines, and I never saw any problems like this again, and I never saw anybody using this rule. In many machines, the dbspaces were defined with the same size of the raw devices, and the raw devices were defined with the same size of the disks. Now I had the same problem with another Sun machine, but this time with a disk array, and with a chunk that was not the rootdbs, and the Sun diagnostic was that I should have created the dbspace with offset. On Informix release notes there is nothing about this in any plattaform. Does anybody have an opinion about this ??? Thanks !!! -- Paulo Roberto Marelli de Amorim TS&0 Consulting Brasil Sent via Deja.com http://www.deja.com/ Before you buy.

Some OSs use the first portion of a disk for its vtoc. Solaris is one. HP-UX definitely doesn't do this, nor does NCR's variant. I can't comment on any others. So, in Solaris, if you're to use the first slice of a disk for an Informix raw device, either start the slice from cylinder 1 rather than 0 in format, or provide a 4k offset with onspaces/onmonitor. It's immaterial what type of dbspace you will create in the slice (rootdbs etc.). In fact, this isn't just a problem for Informix, but for Sybase too, and presumably for any other DBMS that uses raw devices. Neil Truby Londis Stores Hampton Hill, UK Paulo Amorim wrote in message <81lvbj$90e$1@nnrp1.deja.com>... >Hello > >Many people say that we must use offset when creating a dbspace/chunk >located on the first partition of a physical disk, due to problems that >may occur with the disk identification area (magic number). This number >could be overwrited, and then the disk could be lost. > >What is the true in all this ?? > >I had this problem on a Sun machine about 2 years ago. We defined a raw >device with the same size of the disk (2Gb) and created a dbspace with >the same size, and every time the system was rebooted, the dbspace was >lost. The problem was solved by defining a small partition of disk just >to the magic number, and the rest of the disk to the raw device. Some >time after this, Informix Techinical Support told me that we must >always use offset when creating the rootdbspace, and without this we >certainly would have this problem. > >I've seen many other Sun machines, and many other machines, and I never >saw any problems like this again, and I never saw anybody using this >rule. In many machines, the dbspaces were defined with the same size of >the raw devices, and the raw devices were defined with the same size of >the disks. > >Now I had the same problem with another Sun machine, but this time with >a disk array, and with a chunk that was not the rootdbs, and the Sun >diagnostic was that I should have created the dbspace with offset. > >On Informix release notes there is nothing about this in any plattaform. > >Does anybody have an opinion about this ??? > >Thanks !!! > >-- >Paulo Roberto Marelli de Amorim >TS&0 Consulting >Brasil > > >Sent via Deja.com http://www.deja.com/ >Before you buy.

Yes you should always use on offset for creation of the chunks...in aix the first block of data on the lv contains the logical volume control block...this is often corrupted by creation of db slices without using the offset...it isn't that much data...better to be safe then sorry...we are having a problem now because of not using the offset for the rootdbs on one of our informix instances....it is really a pain in the arse to move after the fact....set it up right the first time...saves headache later. peace walter walls Sent via Deja.com http://www.deja.com/ Before you buy.