Re: Raw partitions vs. file system

We are using Oracle Parallel Server and therefore have to use raw files. For backing up we use DLT 4700 (SunSparc2000 box). It takes us ten minutes to do a 'dd if=/dev/vx/rdsk... of=/dev/rmt/2n bs=256k' on a 2 GB raw disk. We do a full hot backup with this method every night, it takes us 3,5 hours for 42 GB raw disks.

If performance matters, try different block sizes for dd. If we used the default value (I suppose that's something like 512 bytes), 2 GB will take more than one hour to go to tape! A further advantage of dd is bypassing the cpu. Ask Sun about that, it may be possible to do a direct data transfer from disk to tape without using memory nor cpu.

Martin Haltmayer

Billy Verreynne wrote:
>
> S V <sv1_at_mindspring.com> wrote in article
> <01bce47d$a431bfe0$c85c0c26_at_sfinance3>...
>
> > > What about backups? To backup raw devices in Unix (when you don't have
> > > any special backup software) you need to use dd - and I won't rely on
 dd
> > > backups for a database.
> >
> > what's wrong with "dd" ???
>
> To my knowledge there are no verification with dd and it is very slow -
> especially if you have to back GB's every month. And having to run dd
> backups for over 24 hours gets to be a problem in a production environment.
>
> > I would rather rely on dd which is absolutely
> > reliable piece of soft furniture, tested over generations than on some
> > third-party tools full of bugs.
>
> We're using a 3rd party X-based tool. Works great! - and it outperforms dd
> by far.
>
> > well, this is simply NOT TRUE.
> > All it takes
> > to move a datafile from /dev/rlv01 to /dev/rlv02
> > is
> > ALTER TABLESPACE AAA OFFLINE;
> > dd if=/dev/rlv01 of=/dev/rlv02 bs=4k skip=1 seek=1
> > ALTER TABLESPACE AAA RENAME DATAFILE '/dev/rlv01' TO '/dev/rlv02';
> > ALTER TABLESPACE AAA ONLINE;
>
> Ah ok - I retract that it's not impossible. :-) But what you fail to
> mention that you must make sure that the raw slices should be the same size
> or else you'll waste space. With file systems you have more flexibility.
> You can have multiple variable size datafiles per file system. With raw
> devices it is a single fixed size datafile per raw slice. Shuffling data
> files around on file systems are much easier.
>
> The biggest problem IMHO is that you require solid Unix skills to
> administer and maintain raw devices - and this is usally outside the scope
> of knowledge required by an Oracle DBA.
>
> > to delete raw device it takes _at least root access to the box.
> > I would never use root account for running a database.
> > To delete a cooked file, it suffices to be only oracle,
> > which is a step lower level of security.
>
> Agreed, but only the DBA should have oracle access. But too often security
> is lax and developers have root and/or oracle access. I don't think that
> security should be a factor when it comes to raw vs cooked files.
>
> regards,
> Billy
Received on Fri Oct 31 1997 - 00:00:00 CST