Re: Backups on raw devices

I have extensive, but aging, experience with hot backups of raw devices on active systems - on Solaris, AIX, HP-UX, and a handful of other Unix variants - and some significant experience with OPS on Sun Cluster.

"dd" works, but certainly isn't "the easiest way" - or the fastest! For one thing it will take a *LOT* longer than any modern backup utility. For example, dd will read the entire device - used or not. RMAN will know how to do "null block compression" - which isn't what it sounds like, but can be significantly faster. If you are on Sun Solaris and already have Veritos Netbackup for the system backups, use Netbackup as the media management layer and RMAN as the backup utility. This is how I've been doing all Oracle backups on Sun for the past 3.5 years. It isn't that hard to set up. RMAN is fairly easy in fact, but Netbackup is generally a bit more complex. Make sure you have your catalogs (RMAN and Netbackup) set up properly and test everything very thoroughly!

The SAs are wrong. What they are thinking of is a normal system backup - what they typically do. In Oracle, you will get an "inconsistent" image of the data file, but that is true with any "manual" hot backup - cpio, tar, cp, etc. It is not a problem - iff the tablespace(s) are in backup mode. (Wasn't there something about this on the OCP exam?)

I have not used "dd" for a few years, but what is this stuff about "skipping the header"? I never did anything like that and I used dd on raw devices for years - on hundreds of systems - and never had a problem with either backup or restore&recovery. I think this is more bad information from the SAs.
[e.g With Veritos volumes, dd if=/dev/vx/rdsk/oradg/<volume_name> of=/dev/rmt0n bs=<some value>]
(NOTE: "bs=.." may be optional! And I don't remember offhand if it is /dev/rmt0n or /dev/rmt/0n in Solaris)

I suspect that your SAs are going to be a problem... I might have to withdraw the Netbackup recommendation! You and the SA(s) will need to be in "perfect harmony" to get it working reliably. My first experience with Netbackup/RMAN|EBU was with a rather unsophisticated (and arrogant) SA. He fought it for months and never did get it working right anywhere... and kept blaming it on Oracle and RMAN/EBU. After he was replaced with a MUCH better SA, we had it nailed down tight on over fifty database servers in under a week.

Seriously, if you can afford OPS, you can afford decent backup software - RMAN and Netbackup or something other than plain old "dd"!

Don Granaman
[OraSaurus]

PS: If you do use Netbackup, be aware of how to modify bp.conf to do a restore the another node should the one where you do the backups fail and you have to restore from somewhere else.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Friday, June 15, 2001 2:37 PM

> We have parallel server running on on a Sun Cluster 2.2 and we are looking
> for the easiest way to perform hot backups. Now, I know that you have to
> use the "dd" command and skip the header at the beginning. Everything I
> read on metalink indicates that you can use basically the same paradigm as
a
> hot backup on cooked file systems. But, the sysadmins here tell me that
the
> raw device can't be backed up if there is any write activity on the data
> file that is currently being backed up. Now we all know that contrary to
> popular belief there is write activity on a data file even when the
> tablespace is in backup mode. Is "rman" or some other block-level backup
> utility the only way to get a reliable hot backup on raw devices? Does
> anybody have any experience with hot backups that are made while the
> database still has active users logged in?
>
> I look forward to everyone's thought on this.
>
> Thanks.
>
> Michael L. Jenkins
> Oracle Certified DBA
> Nextel Communications
> Norcross, GA
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
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> Author: Jenkins, Michael
> INET: Michael.Jenkins_at_nextel.com
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Author: Don Granaman
  INET: granaman_at_home.com

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