RE: Cook device vs Raw device

> > Nothing special you need to do. You can even bring the > engine down, copy > each cooked file to a separate RAW chunk at least as large, > replace the > cooked filename with a symbolic link to the RAW file and restart the > engine. Art, is it possible to migrate this way if filesystem files were specified _without_ offset, but AIX (AFAIK) raw devices must have an offset of a few kilobytes? best regards, ivars > > Performance is usually about 8-15% better with RAW chunks over COOKED > devices and add another 7-10% for filesystem files. So expect 15-25% > improvement. > > Art S. Kagel >

Ivars Strazdins wrote: > > > > Nothing special you need to do. You can even bring the > > engine down, copy > > each cooked file to a separate RAW chunk at least as large, > > replace the > > cooked filename with a symbolic link to the RAW file and restart the > > engine. > > Art, > > is it possible to migrate this way if filesystem files were specified > _without_ offset, but AIX (AFAIK) raw devices must have an offset of a few > kilobytes? > > best regards, > ivars > > > > > Performance is usually about 8-15% better with RAW chunks over COOKED > > devices and add another 7-10% for filesystem files. So expect 15-25% > > improvement. > > > > Art S. Kagel > > Hi Ivars, there is no absolute need to have an offset when raw devices in AIX, although it is better to specify an offset of 4 k. AIX stores some information about the logical volume in the first 512 (maybe 1024 ?) bytes of a logical volume. But it also checks if this area has been overwritten. If yes, it disregards the AIX information that usually is there, but does not try to restore it. So, you just miss some information when looking at the logical volume characteristics. At least that's the theory (and in most cases it works). Regards -- Helmut Leininger Bull AG / Vienna Open Systems Support Email: h.leininger@bull.at helmut.leininger@bull.net This opinion is mine and not necessarily that of my employer. No guarantees whatsoever.