LTO5 Tape only storing 1.4 TB with compress mode on

[MikelSS]

Hi,

I was searching on the internet and in the forum about this issue and I think I have everything configured right, but I really don't get the point. Here is my question.

This is my scenario:

- Tape drive HP StoreEver LTO-5 Ultrium 3000 SAS External Tape Drive/S-Buy (2:1 hardware compression)
- LTO5 Tape (3TB compressed mode??)
- Policy with Compression option checked ( As far as I know it enables the hardware compression)
- Drive density set as HCART2
- NetBackup 7.5

The point is when the backup data reach 1.46 TB (I get that amount reading the software logs) , Backup Exec request another media.

Is that correct?
Is NetBackup compressing the data?

I do not know if I am missing something in the configuration or if just the limit of the tape is 1.5 TB

Thanks and regards.

[Nicolai · Accepted solution]

Hi Mikel

The compress option is not related to tape drive compression. The compress option in Netbackup causes Netbackup to do software compressing of backup data before sending data to the tape drive. Already compressed data will not benefit further compression - that why you are seeing 1.5TB and not 3TB.

A tape drive will compress data by default - you do need to configure anything from Netbackup.

In general software based compression has a bad performance whereas a tape drive does it in the hardware.

Disable compression in the policy and you will get closer to the 3TB per tape.

Netbackup or Backup Exec will request a new tape when the tape drive signal a "end of media" (EOM) to the backup application.

[Ron_Cohn]

The amount of data backed up also depends on the data format.  Text data will compress quite nicely.  JPG's compress very little or not at all.
 

[Marianne]

Compression is only advisable when a client is on a slow network. Even then the effects with and without compression needs to be examined and evaluated.

Have a look at these TNs: 
http://www.symantec.com/docs/HOWTO86618 
http://www.symantec.com/docs/HOWTO56173

[Jim-90]

Some advice from HP that's still relevant <link>

Summary :

• Recompression wastes time and processor power.
• It may actually make the end result bigger instead of smaller.

[MikelSS]

Thanks for all the responses.

I will test the policy with compress option checked/unchecked and evaluate the time/data .

Of course, I will let you know all the results.

Thanks and regards

[jim_dalton]

I would say you have your tape full as per spec. Youve compressed your data at source, it's unlikely to be compressed even more by the drive so the drive receives uncompressible data and youve written 1.46Tb of it, which is give or take the capacity of 1.5Tb.

Jim