Brbackup hardware compression information

[Former Member]

Hi

we are taking backups using brtools.but we are not running compress command (brbackup -k only).in our init(sid).sap file contain compress=no settings.

1.It it compolsury to run compress command every month?if i do not run this command can i restore database successfully or not?

2.For restoration compress option settnings is necessary? what are the settings for compress=' " ?

our sap version is :4.7E and Database is :oracle 9.2 and unix: HP-UX and tapedrive is :HP ultrium

Please kinly help on this

Regards

Nani.

[Former Member]

Hi,

If you are not running with hardware/software compression then it is not necessary to run "brbackup -k only". This command is to inform BRBACKUP/BRARCHIVE of the compression rate so it can calculate how much can go into one tape.

To restore, the compression settings must be the same as during the backup ( if you do a software compression with gzip, then BRRESTORE must know that he has to "uncompress" the files being restored )

[Former Member]

Hi

thank you very much for your suggestions.

but if i take backup without compression can I restore database without errors.

Please kindly reply on this

Regards

nanai

[Former Member]

Hi Nani,

If you use hardware compression, you should set the parameter "compress=hardware" in init<sid>.sap. Also, run a "brbackup -k only" once a month to update the compression rates.

As brbackup does not now about the compression rates of your hardware, it assumes that it is the same as with software compression.

The parameter "compress_cmd" is only needed for the "-k only" run, not for the backup itself.

See e.g. OSS note 13372 or 13550 for more details.

HTH,

Elmar.

Message was edited by:

Elmar Billen

[Former Member]

In our init(sid).sap file contain compress=no we are taking brbackup using DB13,

if i want to restore this data at the time of restore will we face any problem

Regards

Nani

[Former Member]

If you specify "compress=no", brbackup will not be able to compute the amount of data which fits on your tape.

However, if the data does fit on your tape and brbackup finishes successfully, you can restore it without any problems. The compression/decompression is done transparently by your hardware.

In this case, you do not need to run "brbackup -k only"...

HTH and best regards,

Elmar.

[Former Member]

Hi,

Sorry but I think you are wrong.

IF "compress=no", you are telling BRBACKUP that there is <b>no</b> compression involved.

Therefore, if BRBACKUP see that there is a 2GB datafile, it will think all 2GB go to the tape and it will use this <b>full size</b> to calculate the ammount of data that fits on the tape.

For example.

100 data files * 2GB = 200 GB ( lets dismiss other files for the example )

if tape_size is > 200 GB BRBACKUP assumes it fits on the tape

if tape_size is < 200 GB BRBACKUP assumes it does not fit on the tape

This means that BRBACKUP is able to compute the ammount of data that fits on the tape. It does it much better than if there is compression.

If you are using compression then brbackup will have to calculate how much data you are backing up considering the compression rate ( hardware or software ).

In the previous case, you have 200 Gb ( real ) to backup.

Imagine that the DB is newly installed and compression rate is x4

Then BRBACKUP thinks it needs 200/4 = 50GB tape to backup.

Same as before, if you have a tape that fits this size, you do not have problems.

But, if the compression rate is OLD, what happens is that the "real" compression is decreasing as time pass ( you are filling the datafiles, the blocks began to have "information" and it is not so easy to compress )

If you do not update the compression rate with "brbackup -k only" brbackup thinks the compression rate is x4. Still needs 50Gb, but currently, the compression rate is x2 and it will need 100Gb tape.

If your tape is 75Gb, BRBACKUP will reach the end of the tape before he expect and you will have a problem.

Regarding the inital question.

If you are using "compress=no" to backup, then you will have no problems to restore.

[Former Member]

So,I am using the compress=no and at the end brbackup finished with success.plerase see belowlog

BR202I Saving reorg_log

BR203I to /dev/rmt/0mn ...

BR202I Saving /oracle/PRD/sapbackup/bdvifzch.aft

BR203I to /dev/rmt/0mn ...

BR202I Saving /oracle/PRD/sapbackup/backPRD.log

BR203I to /dev/rmt/0mn ...

BR280I Time stamp 2007-05-24 20.52.36

BR226I Rewinding tape volume in device /dev/rmt/0m ...

BR351I Restoring /oracle/PRD/sapbackup/.tape.hdr0

BR355I from /dev/rmt/0mn ...

BR241I Checking label on volume in device /dev/rmt/0mn

BR280I Time stamp 2007-05-24 20.53.41

BR226I Rewinding tape volume in device /dev/rmt/0m ...

BR056I End of database backup: bdvifzch.aft 2007-05-24 20.54.03

BR280I Time stamp 2007-05-24 20.54.04

BR053I BRBACKUP terminated successfully

so i can restore the backup without problems.

Regards

nani

[Former Member]

> so i can restore the backup without problems.

Yes, you can.

@Fidel: you are right. What I wanted to say was: with "compress=no", brbackup assumes that a 100GB tape can hold 100GB of data - using hardware compression there will fit more data on the tape, but brbackup won't use it (unless you set the tape_size to a larger value than the physical size...).

Best regards,

Elmar.

[Former Member]

Thanks & Regards for your valuable suggestions.

Regards

nani