Hi Dave, Using your idea, we did see a drop in the "seconds to archive" - almost half the prior values. We also see a drop in 'log file sequential read' wait event based on AWR data. I think that the 'log file sequential read' waits are when the Arc process is trying to read the Redo logs and creating an archived file on the disk. I also wanted to measure the throughput of the redo logs itself, basically - are we now writing faster to the redo logs. Anyone: Should we be looking at 'log file parallel write' and 'log file single write' waits, or something in addition to these? Thanks, Deepak ----- Original Message ---- From: "Roberts, David (GSD - UK)" <david.h.roberts@xxxxxxxxxx> To: sharmakdeep_oracle@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx Sent: Tuesday, September 9, 2008 3:47:03 AM Subject: RE: Measuring the impact of Redo Log change While the following SQL isnʼt going to be able to tell you anything about the performance of the application you are running, it may give an indication of increased stability, and depending on the size of your control file may give you data from both before and after the change for you to compare. One of the problems I have encountered is when redo logs are all on a single disk device, there will be contention between the archive log process and the log writer, which will be seen in an increasing amount of time taken to archive logs (Iʼm assuming youʼre in archive log mode) when the system is under duress. SELECT recid, To_Char( next_time, 'YYYY-MON-DD HH24:MI:SS' ), (completion_time - next_time) * ( 24 * 60 * 60 ) "Seconds to archive" FROM v$archived_log ORDER BY recid If the peek or average time to archive logs has dropped, it would be possible to argue that you have increased the theoretical throughput! Obviously if you had the opportunity, placing redo log groups on alternating physical devices would obviously be a better way to reduce this form of contention! Dave David Roberts _________________________________________ Logica- Releasing your potential www.logica.com Logica UK Limited Registered in Englandand Wales(registered number 947968) Registered office: Stephenson House, 75 Hampstead Road, LondonNW1 2PL, United Kingdom -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Deepak Sharma Sent: 09 September 200805:33 To: oracle-l@xxxxxxxxxxxxx Subject: Measuring the impact of Redo Log change We recently (today) moved the redo logs from RAID5 to RAID1+0. The obvious reason of doing this is to make things better in terms of performance, as RAID1+0 is better suited for read/writes. Someone pls correct me if that's not true. What are different ways to measure the impact of this change? The platform is AIX, DB is 10.2.0.3 and DB size is 55TB, and 2TB redo is generated each day. There are plans underway to reduce the redo generation using direct path etc. (so let's not get diverted by that). We can try measuring the wait event stats using AWR, session stats etc., but what exactly to look for? 'log file switch completion', 'log file sync', are some things that come to mind - what else? Thanks, Deepak This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.