What is the measure for tablespace IO writes efficiency?

[nir_s]

Hi guys,

We've started transferring in the last days our storage from DMX3 to Vmax.
I want to compare performance of specific tablespace before and after the transferring.
In AWR ,in the section of Tablespace IO stats I checked the measure "Av Rd(ms)" regarding reads.
Is there a measure for writes?
How can I know that I've got an improvements regarding writes?

Thanks in advance,
Nir

[LKBrwn_DBA]

How about "Av Buf Wt(ms)"?
Also maybe you want the Average ms it take to read one block which is:

Av ms/blk = Av Rd(ms) / Av Blks/Rd

[nir_s]

Hi,

Thanks!
Av Buf Wt(ms) is a threshold value for measuring Buffer Busy Waits.
It's not related necessarily to writes watings.

[PAVB]

Provided timed_statistics is set to TRUE v$filestat shows the information you are looking for.

Having said that, please take into consideration that Write I/O performance is a tricky matter in the sense that:

1- Writes to datafiles are done by DBWR in the background so as long as DBWR can keep up with the load you really don't care about I/O performance;; DBWR will get it done and user community will never notice performance fluctuations.

2- Writes to logs and temporary segments on the other hand are done in the foreground therefore poor performance in such segments will immediately have a negative impact on overall performance.

Bottom line, don't waste your time analyzing Write I/O on standard "data and indexes" data files; focus your attention on Logs or Temporary segment data files.

Last but not least, when looking at Write I/O I would suggest to check what's the performance your I/O subsystem is giving you - talk to your storage guy and ask her/him to report 'service levels" to you. Also ask for the technical specs of your particular I/O subsystem so to compare what the vendor sold against actual service levels.

Hope this helps.

[nir_s]

Thanks a lot Pablo!
You were very helpful

Best regards,
Nir

[stecal]

Which release of Oracle are you using? You can gather IO stats (via dbconsole/gc is one way, one-click button to have Oracle collect that info).

[nir_s]

Thanks stecal