Hardware compression on MSL 6060

[Vincent_Chua]

Our current environment setup is:
(1) Tape Library - HP MSL 6060
(2) Tape Drives - HP Ultrium-2 Tape drives x 2
(3) Backup Server - Veritas Netbackup Enterprise server on Windows server 2003

One of our backup policies is to backup Oracle database using RMAN to tapes. On one occasion, the backup fails giving a tape full error. When we look into the media contents, there were 2 backup sets in the tape; 1 backup set is about 150GB and another only about 16MB. The failure occurs when Netbackup attempt to backup another file of about 60GB into the same tape. The total size of that backup job should be around (150GB + 16MB + 60GB)=210GB.

We are using LTO-2 tape and only 1 tape is assigned to that backup policy. At the same time, we have turned on hardware compression on the tape library. We did not turn on software compression on Veritas Netbackup. Given that the backup size is 210GB and having hardware compression turned on, we would expect the backup to go through successfully but it fails instead. Can anybody please comment what has gone wrong? Thanks.

[VCP2005]

Hi Vicent,
The compression rate is alway x 2 and depend. If you have compression rate of 1.3 then LTO2 will have 260GB only.

Please give more details for e.g.
1. what is the backup error code
2. backup media retention

[Vincent_Chua]

Hi Weng Keong,

Thanks for the reply. My question is rather directed at why is hardware compression so low for Oracle RMAN backup. Based on your reply, it seems like we don actually get 50% compression everytime.

[Marino Meloni_1]

May be you have double compression enable, this will increase the overhead and the data will be larger that normal, I have read that RMAN include now a binary compression, try to use or the RMAN compression, or the Netbackup SW compression, or the HW compression, but only one at a time:

see article:
_____________________________________
Compressed Backupsets
10G RMAN now supports binary compression of backupsets. Administrators activate compression by specifying the AS COMPRESSED BACKUPSET parameters in the BACKUP command. Oracle states that the backupsets are compressed using an algorithm that is optimized for efficient compression of Oracle database datafiles.

What I like most about this feature is that you don't need to uncompress the file to use it as input to an RMAN recovery. RMAN will automatically uncompress the file during the file restoration process.

Oracle states that compressing the output file does increase CPU overhead for both the backup and restoration processes. Since the majority of our backups are sent directly to tape devices, having RMAN generate smaller backup files is not really a huge benefit to us. But there are times when we need to send a database backup to disk for performance reasons. Like many shops, we never seem to have enough disk available for the backup's output files. We are hoping that the compression utility will help us when we need a backup immediately and are pressed for space.

We'll run one backup with compression off and another with compression activated and compare the size of the output files. We will then use the compressed backup as input to an RMAN recovery to make sure it works. I'll let you know the results as soon as we have them!
__________________________________________

[Marino Meloni_1]

http://www.oracle.com/technology/deploy/availability/htdocs/rman_overview.htm
forgot also a link

[Vincent_Chua]

Hi Marino,

Thanks for the reply. Its definitely helpful.

[VCP2005]

Hi Vincent,
By default (without any configuration at RMAN), ORACLE RMAN should backup backup set by min ~2x compression rate.

The tape full error message might cause by NetBackup, may I have more detail on NetBackup
a. what is the error code u got ? 96 ?
b. bpmedialist
c. do you set different retention level at different day ? or Does this problem happen on certain day e.g. Sat
d. vmpool -listall
e. tpconfig -d

LiewWK