dww@stl.UUCP (David Wright) (09/26/86)
Back in 1981, when VMS was 2.2 and our VAX 750 had only got RK07's on it, the disks were initialised with the default cluster size of 3. I guess that was OK for those circumstances: at least there wasn't a fresh allocation of space every block. Though some '730s I know of do have the cluster size set to 1, to make every block available. Since then we have gone to RM80's, RA81's, 400MB Eagles and (shortly) 600M Super-Eagles, and VMS/RMS has advanced too, in particular allocating lots of blocks at a time (e.g. 81) then trimming off the unused ones (modulo the cluster size). But we still have cluster size=3 on all our disks, (except on some MicroVAXen which use 1), because that still seems to be the default. Now to the point: does anyone know whether cluster size is important now, and if so what values should be used in what circumstances? Has anyone made any measurements of the performance impact etc.? Except for a few big indexed files (which are designed with FDL etc.), almost all the files on our VAXen are simple variable length record sequential files, mostly small, but with enough larger ones to make the disk fragmentation we are currently seeing a nuisance.