File Data Compression issue
Currently we are using Symantec NetbackUp 7.6.0.4 for master/media server and for the backup clients, running under Windows Server 2012 R2 Standard. Tape library is Dell PowerVault TL4000 with LTO 6 tape cartridges for backup duplication. We all knew that LTO 6 can accomodate up to 6.25TB capacity. However, the duplicated file only eats up around around 2.5TB and shows in the Media Status is 'Full' . Refer to the snapshot below:
It seems that the compression does not work. Please help, thanks.
LT06 actually accomodate 2.5Tb, yes with compression it can accomodate an absolute maximum of 6.25.
Some files will compress better than others, it maybe that the files you are backing up don't have a good compression ratio, such as data files. What type of data are you backing up?
See the end of this post:
https://www-secure.symantec.com/connect/forums/problem-tape-cartridge-usability
FYI - to achieve and sustain 6.25TB on an LTO6 is fairly unusual. Most sites typically see (on average across a large pool of media) ratios of 1.1:1 to 1.4:1 capacity - sometimes some media are 1:1, sometimes others are 1.8:1.
The fact that you are achieving exactly the quoted native capacity of LTO6 says to me that your data is compressed and/or encrypted before it reaches NetBackup.
Questions:
1) Is the source data made up of any of these:
Jpeg, mpeg, mp3, zip files, compressed database dumps, encrypted database dumps, or any form of pre-compressed or pre-encrypted data?
If the bulk of the data being backed-up is any of the above then your capacity results are entirely normal.
2) If you still think your data is highly compressible, then have you checked your backup policies to see whether you have already selected client side compression or client side encryption? If you have then your tape capacity results are entirely normal.
I would remove that compression tick in the policy and let the tape drive do the work. The drive will do it in hardware very efficiently and you wont get any degredation in performance.In fact you might get improved performance as the drive will try to compress the compressed stream. This will remove the compression load on the client and speed up your backups.
Jim
I agree with Jim Dalton. With modern LTO tape drives, there is no advantage to using the Netbackup software compression in your policies. The tape drive hardware-based compression is more efficient and uses less resources in your clients and servers.
If tape drive compression is configurable in your tape library (I've never seen that it was configurable in the libraries I've used), ensure compression on your tape drives is turned on and uncheck the compression box in the NBU policies.
Also, that is why your tapes only appear to hold 2.5TB now. If compression was already turned on in the policy, NetBackup compressed the data before sending it to the tape drive, which can't compress it any further. I'm guessing that if you added up all the data in the images written to those tapes, it would be more than 2.5TB.
