Re: DBEXPORT question

Ivan Lopes Junior wrote: > > Hi Kerry, > > About the workload: You are spreading the workload when you use the RAID > 5.The RAID 5 writes one block in one disk (you can configure that I think > in my environment is 64K) and then the RAID "jumps" to other disk and so > on. > I really don't know this dbspace internal overhead you mentioned but if you > find out something please let me know. > > About the RAID cache:Yes.You must have at least 32Mb in the RAID > cabinet.You shoud check it to avoid the bad writing performance. > > Regards, > Ivan > ---------- > De: Kerry Davids[SMTP:dino@ix.netcom.com] > Enviada em: Domingo, 22 de Junho de 1997 02:03 > Para: Ivan Lopes Junior > Assunto: RE: DBEXPORT question Hi Ivan, I would suggest to create several dbspaces, even if you are using a RAID 5. 1st: Have you tested, when Informix performs PDQ ? Don't you think, parallel scans are required for parallel data query ? Parallel Scans will be used only on fragmented tables. 2nd: If you have a very large table ( 1 million rows ) and if you would spread the rows on two dbspaces, i.e. 95% to dbs1 and 5% to dbs2: fragment by expression f1 < 1000 to dbs1 -- 95% of all rows f1 >= 1000 to dbs2 -- 5% of all rows How many rows must be read, if you run the following query ? select * from table where f1 >= 1000 Do you agree, that fragmenting your table across seperate dbspaces might speed up your queries ? Finally, I don't think that every RAID 5 Controller can use the built-in cache to speed up write activities. When the data written to disk will reach the controller, the controller can't send an acknowledge back to the OS, unless there is a battery on your controller which ensures, that the data inside the cache can be flushed to disk in case of power fail. Bye Stefan