RE: Raw device VS cooked file - any benchmark recently done?

I would really like to see any evidence that people have on this issue. I have a number of systems that are running with acceptable performance on raw disks. But could we be doing better and at what cost? But from almost 20 years of working with this disk architecture and with lots of other architectures I have discovered that the performance that you can get out of a disk system is in almost direct proportion to the amount of time that you, the administrator, put into it. If you want the ultimate performance then spend a lot of time doing the systems engineering - but if you can get acceptable performance without doing much then so be it. Many modern disk architectures can give you acceptable performance without raw disk - now. But will that continue when the UNIX file system gets more fragmented? And what are the other reasons for using raw disk - think about backup and recovery as well. Regards Malcolm -----Original Message----- From: informix-list-bounces@iiug.org [mailto:informix-list-bounces@iiug.org] On Behalf Of Rupan3rd Sent: 10 January 2006 14:50 To: informix-list@iiug.org Subject: Raw device VS cooked file - any benchmark recently done? Hi everybody, a question about raw VS cooked once again (sorry about that), hopefully this time a bit different. I am using IDS 10.0 on Red Hat Enterprise Linux version 4, as well as on Solaris 8 and 9. I use Informix since years, and always have installed it making use of raw devices, since there always have been a clear statement in the IBM documentation telling that on UNIX raw devices are the suggested choice for the best I/O performance. The IBM IDS 10 Server Administrator Guide, http://publib.boulder.ibm.com/epubs/pdf/25122672.pdf, at page 241 says infact: --------------------------------------------------------------------------- <<On UNIX, you should use raw disk devices to store data whenever performance is important.>> --------------------------------------------------------------------------- However, looking further in the same document, at page 242, I have noticed that for the first time there is also this new and interesting statement: --------------------------------------------------------------------------- <<Important: While you should use raw disk devices on UNIX to achieve better performance, recent advances in I/O caching for cooked writes can provide similar if not better performance. To determine the best device performance, perform benchmark testing on the system with both types of devices for the dbspace and table layout.>> --------------------------------------------------------------------------- This last sentence was not included in the previous versions of the documentation (checked for IDS 9.4). I have been googling around, finding out on the IIUG repository that the measured performance of raw VS cooked VS cooked on filesystem is roughly X, X-20%, X-35% respectively. Source of these figures: http://www.iiug.org/resources/cdi_archive/2005.05/cdii.137120 I was wondering if anyone have recently done a benchmark using IDS 10 on UNIX configured with raw areas versus the same engine configured to use cooked files over filesystem, where the cooked file is stored on a device where "I/O caching for cooked writes can provide similar if not better performance". In other words, I would like to understand if that is really true and what feature should the disk device or SAN have in order to meet the requirements of being good in "I/O caching for cooked writes". One last thing I don't understand is if, in case there is a device capable to be good in "I/O caching for cooked writes", it would be equally good in cooked READS. Any feedback would be appreciated. Thanx in advance, Rupan3rd (from Italy) _______________________________________________ Informix-list mailing list Informix-list@iiug.org http://www.iiug.org/mailman/listinfo/informix-list