Re: Oracle-managed RAID-like tablespaces

To improve the performance on the multiple disk, use the hardware RAID controller. you can do RAID 0 + 1 at the hardware level. Then use the VM to create the logical volume. Because of the hardware raid stripe and mirror, the os or oracle could not able to see the physical disks.

Purna
Oracle DBA/ Unix Sysadmin.

"Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:<65b19.46858$Hj3.142494_at_newsfeeds.bigpond.com>...
> Hi Roobaron,
>
> Output from a table I created in a LMT that has two datafiles associated
> with it. I made sure the table would require multiple extents when created.
>
> SQL> col segment_name format a15
> SQL> select segment_name, file_id from dba_extents where segment_name =
> 'STRIPE';
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
>
> 40 rows selected.
>
> There seems to be a pattern occurring !!
>
> Then issued the following:
>
> SQL> alter table stripe allocate extent;
>
> Table altered.
>
> SQL> /
>
> Table altered.
>
> SQL> /
>
> Table altered.
>
> SQL> /
>
> Table altered.
>
> SQL> select segment_name, file_id from dba_extents where segment_name =
> 'STRIPE';
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
>
> SEGMENT_NAME FILE_ID
> --------------- ----------
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
> STRIPE 9
> STRIPE 11
>
> 44 rows selected.
>
> And the pattern continues !!
>
> If you re-read the horses mouth, it says "by first determining a candidate
> datafile in the tablespace" which is indeed in a round robin fashion (and
> has been for a long long time).
>
> Now I agree with previous comments that such physical layout should
> preferable be performed at the O/S level, but at least Oracle does have a
> reasonable method of manual striping that could be useful in distributing
> data across a desirable number of devices.
>
> Hopes this clarifies
>
> Richard
>
> "roobaron" <member_at_dbforums.com> wrote in message
> news:3d4533a6$1_at_news.usenetgateway.com...
> > Had a quick look at the doco (concepts manual) for 8.1.7 doesn't mention
> > that data is written in a round robin fashion, the algorithm will write
> > to the same datafile as long as there is contiguous space, only looking
> > at the other datafile if there is not enough space.
> >
> > Here it is from the horse's mouth
> >
> > "Allocating Extents in Locally-Managed Tablespaces In locally-managed
> > tablespaces, Oracle looks for free space to allocate to a new extent by
> > first determining a candidate datafile in the tablespace and then
> > searching the datafile's bitmap for the required number of adjacent free
> > blocks. If that datafile does not have enough adjacent free space,
> > Oracle looks in another datafile."
> >
> > What you are trying to achieve is striping for reads... we are talking
> > somewhere in the vicinity of 8k reads per I/O depending on the disk I/O
> > setup. To stripe the data exactly so that your app gets the multiple
> > disk heads retrieving via Oracle is not worth the effort.
> >
> > Use OS striping or a decent LVM as mentioned.
> >
> > Hope this helps save time
> >
> >
> >
> > --
> > An Oracle DBAs undocumented init.ora parameters
> > _OVERCOME_POOR_DESIGN = TRUE
> > _DISABLE_BAD_PERFORMANCE = TRUE
> >
> > Posted via dBforums
> > http://dbforums.com
Received on Tue Jul 30 2002 - 20:54:14 CDT