Re: How fast should an IO be on a SYMMETRIX?

Hello Jonathan,

You are quite right about 10ms being a reasonable number. The original poster's timing, however, is closer to 100 ms and that's not an indication of his Symmetrix good health.

Rgds.

"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message news:bnlevm$f93$1$8302bc10_at_news.demon.co.uk...
>
> How fast are the discs in the Symmetrix ?
> Forget the b/s that EMC will give you about
> the massive cache - at some point you have
> to be hitting disc.
>
> Your rate of 10 ms per read is pretty reasonable
> for random, non-cached I/O, unless you happen
> to have the newest fastest discs on the market.
>
> Remember, too, that if you are using a Symmetrix,
> you may have no idea whatsoever about the other
> I/O that is hitting the same discs at the same time.
> James Morle has written a paper entitled Sane SAN
> that discusses the issues of black boxes like the
> Symmetrix.
>
> --
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> The educated person is not the person
> who can answer the questions, but the
> person who can question the answers -- T. Schick Jr
>
>
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>
> "Scott Watson" <nospam_at_hotmail.com> wrote in message
> news:0Ugnb.31717$Pt3.792770_at_weber.videotron.net...
> > Group,
> >
> > I have the following query.
> >
> > select a.*
> > from
> > golfowner.scott_match_data a,
> > (select * from golfowner.t_mtch_subj_id where rownum < 50) b
> > where
> > a.wb_ctry_cd = 785
> > and a.subj_id = b.subj_id
> >
> >
> >
> > Using tkprof to collect waits for the above query I found that the
> read time
> > is what is impacting performance of this query. I would like to
> know if
> > these times are realistic for a lightly loaded server.
> >
> > The database is a 2node RAC cluster running HP-UX 11.11 with raw
> partitions
> > on
> > a Symmetrix. Does my Symm need a check up or is there some setting
> I can
> > change
> > to increase the read IO. ( Async IO is already set up )
> >
> >
> >
> > Thanks,
> > Scottt Watson.
> >
> >
> > select /* new */ a.*
> > from
> > golfowner.scott_match_data a,
> > (select * from golfowner.t_mtch_subj_id where rownum <
> :"SYS_B_0") b
> > where
> > a.wb_ctry_cd = :"SYS_B_1"
> > and a.subj_id = b.subj_id
> >
> > call count cpu elapsed disk query current
> > rows
> > ------- ------ -------- ---------- ---------- ---------- ----------
> ------
> > ----
> > Parse 1 0.00 0.00 0 0 0
> > 0
> > Execute 1 0.00 0.00 0 0 0
> > 0
> > Fetch 33 0.06 2.50 254 736 0
> > 473
> > ------- ------ -------- ---------- ---------- ---------- ----------
> ------
> > ----
> > total 35 0.06 2.50 254 736 0
> > 473
> >
> > Misses in library cache during parse: 1
> > Optimizer goal: FIRST_ROWS
> > Parsing user id: SYS
> >
> > Rows Row Source Operation
> > ------- ---------------------------------------------------
> > 473 TABLE ACCESS BY INDEX ROWID SCOTT_MATCH_DATA (cr=736 r=254
> w=0
> > time=2497285 us)
> > 573 NESTED LOOPS (cr=299 r=36 w=0 time=239305 us)
> > 99 VIEW (cr=36 r=0 w=0 time=660 us)
> > 99 COUNT STOPKEY (cr=36 r=0 w=0 time=527 us)
> > 99 TABLE ACCESS FULL T_MTCH_SUBJ_ID (cr=36 r=0 w=0
> time=396 us)
> > 473 INDEX RANGE SCAN SCOTT_MATCH_DATA_IX01 (cr=263 r=36 w=0
> > time=237472 us)(object id 45838)
> >
> >
> > Elapsed times include waiting on following events:
> > Event waited on Times Max. Wait
> Total
> > Waited
> > ----------------------------------------
> > Waited ---------- ------------
> > SQL*Net message to client 33 0.00
> > 0.00
> > global cache cr request 108 0.00
> > 0.03
> > SQL*Net message from client 33 0.00
> > 0.03
> > db file sequential read 254 0.45
> > 2.42 <<<<< ALL THE WAITING IS HAPPENEING HERE.
> >
> >
>
>
Received on Tue Oct 28 2003 - 05:30:27 CST