Bruce, Thanks for your response. Btw, our platform is HP-UX. I put some comments inline below... On Tue, 16 Nov 2004 13:23:22 -0700, McCartney, Bruce <bmccartney@xxxxxxxxxxxxxxxxxxx> wrote: > 1) raw devices performed better ('log file parallel write') than solaris ufs > by between 10 and 20% on average time over long periods. I think this is > notion is supported by steve adams notes. ------ We are also on raw devices - first of all, because all our DB are RAC. > 2) the drives were mirrored in the EMC array and we were told by EMC that the > array will perform sequential reads (ARCH copies) from the 'mirror' as to not > introduce measurable contention. We did not confirm this technically but > were unable to see any contention when ARCH was active reading. so this may > not be a critical issue for you. Are you spending a lot of time in log file > sync? There may be other reasons why... ------ Our mirroring is implemented differently for HA. We use separate storage arrays, controllers, networks, and independent physical location. So we wouldn't benefit from mirroring. I think that some of DBs have too large log_buffer that leads to extensive 'log file sync' waits. > 3) the array provides a degree of isolation from physical writes to a point > by memory caching, but there is a limit of a number of writes that can be > pending on any one drive in the array. because of this behavior, our emc > tech specialist advised us to stripe the redo rather than but it on a > separate disk pair in the array. I can't recall the stripe size off hand... ------ I am not quite comfortable with understanding caching in EMC. I don't understand how it's implemented - per controller/LUN/disk... Would be greate if anyone can recommend a good paper on EMC architechture and caching implementation. -- Best regards, Alex Gorbachev -- //www.freelists.org/webpage/oracle-l